Contagious Summary: 10 Best Lessons from Jonah Berger

Quick Summary: Contagious is a must-read book for marketers who want to create viral advertising. Jonah Berger reveals how you can create marketing that gets remembered and messages that get shared. The 6 principles are: social currency, triggers, emotion, public, practical value, and stories.

It feels like every marketing expert today is talking about social media. 

Why? Because everyone loves the idea that people will promote your business for free. And It’s true that word of mouth marketing is powerful for business. Studies have shown:

Word of mouth is the primary factor behind 20 percent to 50 percent of all purchasing decisions.

Yet most people who put up a Facebook or Twitter page get almost no likes or shares. (Not counting your family!)

What went wrong? Why does nobody care? And how can you make people pay attention and share your stuff?

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If you want people to share your idea, message or business, then you need more than a Facebook page. You need to understand the psychology behind what makes people share.

And I have some good news!

Jonah Berger, a Wharton school of business professor, spent years studying what makes people share and he boiled down all his research into six simple principles.

These are six powerful ways to make your idea, product or business contagious. And by the time you finish reading this page, you too will know how to make your ideas spread across the world infecting minds like a virus. In a good way, of course.

1. Social Currency: “We share things that make us look good”

style fashion image
People like to share things about themselves. Scientific studies have shown we’re actually wired to find self-sharing pleasurable.

Yet what makes people share some things about themselves more than others? In other words, when your friend posts on Facebook, how do they choose what to share with everyone? Jonah Berger says that:

We share things that make us look good. (…)

When we talk to others, we’re not only communicating information; we’re also saying something about ourselves. When we rave about a new foreign film or express disappointment with the Thai restaurant around the corner, we’re demonstrating our cultural and culinary knowledge and taste.

Word of mouth, then, is a prime tool for making a good impression–as potent as that new car or Prada handbag. Think of it as a kind of currency. Social currency. Just as people use money to buy products or services, they use social currency to achieve desired positive impressions among their families, friends and colleagues.

Everybody has a desired identity. It’s how they want to be seen by others. This desired identity controls what shoes someone buys, what car they drive and what music they (publicly) listen to. If you’re a 20-year-old guy, then you probably want to buy a two-door fast car. If you’re a 40-year-old mom, then you probably want to buy a minivan or SUV to fit all your kid’s soccer gear. This is how your choices signal your desired identity to others.

Most people don’t realize this desired identity also controls what people talk about and share with others! People want to be seen as popular, attractive, successful and cool. They don’t want to be seen as forgotten, ugly, poor losers.

  • That’s why people take a video of themselves working out at the gym, but not when they go on a Netflix marathon.
  • That’s why you see photos of beautiful restaurant meals on Instagram, but never a $2 McDonald’s burger.
  • That’s why people will often share messages almost everyone agrees with like “Racism is bad”, but rarely a truly controversial opinion like “Marriage is bad.”

Jonah Berger says: “We share things that make us look good.” That is a powerful insight. It’s worth writing that idea down and keeping it in front of you next time you write a social media post, marketing email or advertising campaign.

We all sort of know this is how social media works, yet we don’t act like we understand it. Most businesses do not stop to think whether sharing their next message will make their customer look good. It starts with asking yourself:

How does your customer want to be seen by others?

Here’s a company that got it right:

Yogi Surprise is a monthly subscription box for yoga lovers. You sign up for $45/month and receive a monthly box full of yoga-related goodies. Yoga books, organic cookies, herbal creams, etc.

Think about what type of person signs up for a monthly yoga box. Many of them want to be SEEN as spiritual, natural and healthy. So they feel great sharing their purchase with others. It fits how they want other people to see them.

The Yogi Surprise website even highlights all their customers sharing photos on Instagram:

yogi surprise social media

That’s all free marketing!

[key-point]Think about what your customer’s desired identity is. How do they want to be seen by others? And how can your product help them create that desired impression?[/key-point]

2. Surprise makes us share, here’s how to create it

surprise spark idea creative

Another way to create Social Currency is through surprise. People like sharing stuff that is new or surprising.

Sharing, extraordinary, novel, or entertaining stories or ads makes people seem more extraordinary, novel, and entertaining. It makes them more fun to talk to, more likely to get asked to lunch, and more likely to get invited back for a second date.

For example, one of the most popular Youtube videos EVER comes from the TV show “Britain’s Got Talent.” It’s a video of a woman named Susan Boyle singing in public for the first time. This video alone has over 215,000,000 views! Why is it so popular? Because it’s surprising!

Susan Boyle isn’t pretty and when she walks on stage everyone expects her voice to match her appearance. Then she opens her mouth and has one of the best voices the judges have ever heard. Everyone is amazed. Have a look yourself:

How to create surprise

To create surprise you have to break expectations. As Jonah puts it:

One way to generate surprise is by breaking a pattern people have come to expect.

If a supermodel had sung like Susan, the video would not be nearly as popular. Why? Because people expect that a beautiful woman will have a beautiful voice. They also expect an unattractive woman to have an unattractive voice. When their expectation is shattered, they feel surprised.

And after someone is surprised by Susan’s voice, they immediately want to share the experience. They want to see the shocked expressions on their friend’s and family’s faces.

Blendtec: How to make a boring product surprising

Even if your product itself is boring, you can often find some creative twist that makes it surprising and worth talking about.

A great example of is Blendtec, a company that makes blenders.

Think about how most blender companies try to advertise. They may talk about how powerful their blender is, how easy it is to use, or how quickly it can be cleaned. Unfortunately, this kind of advertising is boring, so people won’t share it.

The founder of Blendtec had a different idea. A brilliant idea. He started a Youtube channel called “Will it Blend?” where he puts anything and everything into a blender to see if it will blend. Marbles, golf balls, iPhones, anything.

Are you curious to see if an iPhone will blend? You probably are. At the very least, you want to see who’s crazy enough to blend their new $700 iPhone.

Blendtec was making blenders since 1999. Yet for years nobody really knew about them. One day the founder decided to make these videos and they were an instant hit, getting 6 million views in the first week alone. The best part was the videos are not only fun to watch and easy to share, but they also highlight the strength of Blendtec’s blender. After these videos went viral their retail blender sales have increased by 700 percent.

The videos are shared because they are surprising. People expect to see veggies in a blender, not golf balls. And if someone could make a boring product like blenders surprising, then it’s possible to do it with almost any product or service. Here are a couple of helpful tips from Jonah:

The key to finding inner remarkability is to think about what makes something interesting, surprising, or novel. Can the product do something no one would have thought possible (such as blend golf balls like Blendtec)? Are the consequences of the idea or issue more extreme than people ever could have imagined?

[key-point]To increase sharing, generate surprise. And to surprise people, you’ll need to show them something new and different. Something that breaks the normal pattern of what they are expecting.[/key-point]

3. Exclusivity: we want things we can’t have

special unique exclusive hands share

Want to know how to instantly make anything more popular?

Restrict access to it.

That’s right. When you make a product more difficult to get or more exclusive, people want it more.

If something is difficult to obtain, people assume that it must be worth the effort. If something is unavailable or sold out, people often infer that lots of other people must like it, and so it must be pretty good. (…)

People evaluate cookbooks more favourably when they are in limited supply, find cookies tastier when they are scarce, and perceive pantyhose as higher end when it’s less available. (…)

Do you remember standing in a line outside a bar or club for 20 minutes, then you walk inside and discover the place is almost empty? I sure do. Creating a fake line outside is a common trick that bar owners use. People walking by will think the bar is popular. And they assume it is popular because it’s good. So more and more people will join the line.

Here’s another example…

When McDonald’s first introduced the McRib sandwich, it was a failure. They eventually took it off the menu because it was one of their least popular products. However, there were a few customers who loved the taste of the McRib and kept asking McDonald’s to bring it back.

A decade later, however, McDonald’s figured out a clever way to increase demand for the McRib. It didn’t spend more money on advertising. It didn’t change the price. It didn’t even change the ingredients. It just made the product scarce.

McDonald’s brought the McRib back but only made it available for a short time each year. This one change made the McRib incredibly popular. Another example of how people desire things that are limited and exclusive.

Exclusivity not only makes people want your product more, it also makes people more likely to share your product.

Scarcity and exclusivity boost word of mouth by making people feel like insiders. If people get something not everyone else has, it makes them feel special, unique, high status.

And people want to show off their unique status to others because it makes them look good. It’s another form of social currency.

That’s why people will stand outside the Apple store all night to buy the newest iPhone. Later they can show it off and brag to their friends about it.

[key-point]So think about how you can make your product more exclusive or limited. If people feel special just because they were ABLE to buy your product, they will often share it with others because it makes them look good.[/key-point]

4. Triggers help people remember and share

thought link images

Have you ever seen a Youtube music video called “Friday” by Rebecca Black?

It’s an amateur music video made by a high school girl. She’s singing about how it’s Friday and the weekend and she’s going to have fun with her friends. The song is very repetitive and poorly written. It’s so bad that it’s funny to watch. And the video became a huge internet hit, amassing millions of views in just a few days. (The video now has over 110 million views.)

And here’s the most interesting part…

The music video continues to get views today and there’s a spike in views every Friday. On Friday, more people remember the video and show it to their friends. This is a clear example of a trigger. The day of the week (Friday) triggers people’s memory about that funny music video they saw called “Friday.”

Why is this important?

Because if you want to make people talk about your idea, product or business over the long term, then you need to somehow trigger their memory. If people don’t remember or think about your product when they are with friends, then they can’t talk about it. And you won’t receive any word-of-mouth marketing.

It’s actually not that difficult to make people remember your product. People’s memories are constantly being triggered by what’s around them.

If you see a puppy while jogging in the park, you might remember that you’ve always wanted to adopt a dog. If you smell Chinese food while walking past the corner noodle shop, you might start thinking about what to order for lunch. Or if you hear an advertisement for Coke, you might remember that you ran out of soda last night. Sights, smells, and sounds can trigger related thoughts and ideas, making them more top of mind.

Now let’s look at some examples of how to design a new trigger…

How to trigger students into eating veggies

A University wanted to help its students eat more vegetables. So they tested two different slogans for healthy eating. They wanted to see if either slogan would make a difference in the students’ eating habits.

One group of students saw the slogan “Live the healthy way, eat five fruits and veggies a day.” Another group saw “Each and every dining-hall tray needs five fruits and veggies a day.” Both slogans encouraged people to eat fruits and vegetables, but the tray slogan did so using a trigger. The students lived on campus, and many of them ate in dining halls that used trays. So we wanted to see if we could trigger healthy eating behavior by using the dining room tray to remind students of the slogan. (emphasis added)

The results were clear: The “tray” slogan caused students to eat 25 percent more fruits and vegetables, but the “healthy eating” slogan had no effect. When students were in the cafeteria looking at their tray, they must have remembered the healthy eating message. So the trigger worked.

Here’s a different example. This one about how a trigger can be used to promote unhealthy eating.

Give me a coffee and a… Kit Kat bar?

Kit Kat candy bars had become very successful using the “give me a break” advertising campaign. But in 2007 that message had become old and now Kit Kat sales were declining 5% per year. Not good.

Hershey gave Colleen Chorak the job of saving Kit Kat by creating a fresh new ad campaign.

Her idea? She wanted to make people think of Kit Kat every time they had a coffee. She wanted to link the ideas together in your mind and turn coffee into a trigger for the Kit Kat candy bar. So that’s how she designed her radio advertisements.

The radio spots featured the candy bar sitting on a counter next to a cup of coffee, or someone grabbing coffee and asking for a Kit Kat. Kit Kat and coffee. Coffee and Kit Kat. The two spots repeatedly paired the two together. The campaign was a hit. By the end of the year it had lifted sales by 8 percent. After twelve months, sales were up by a third. Kit Kat and coffee put Kit Kat back on the map. The then-$300 million brand has since grown to $500 million.

Many people drink coffee once or twice a day. And each time they did, they might remember the radio commercial about coffee and about Kit Kat bars.

Now you know why so many companies give away free pens, cups, and calendars. If a dentist gives you a calendar, then you might remember that it’s time for you to make an appointment while you’re writing down your parent’s birthday.

Remember, if you’re thinking about something, then you’re likely to talk about it. As Jonah says, “Top of mind, tip of tongue.”

[key-point]Think about what the trigger for your product can be. Is there a common object in your customer’s daily life that you can link to your product?[/key-point]

5. How to “poison” a powerful brand with a negative trigger

the lost art of practice

In 1954, Philip Morris wanted to sell his “Marlboro” cigarettes not just to women, but also to men. The ad agency Leo Burnett created a powerful symbol to use in his advertising. It was the birth of “The Marlboro Man.”

“The Marlboro Man” symbol and ad campaign was immediately a huge success. In the first year, Marlboro sales increased by 3241% to $5 billion! The next year sales shot up to $20 billion. The rugged and masculine image of “The Marlboro Man” was a slam dunk.

Marlboro cigarettes had become a trigger that made guys think of the rugged and masculine image of “The Marlboro Man” who they wanted to be like.

Many decades later, the State of California wanted to make people smoke less by hijacking this powerful branding. They used the same iconic images of a cowboy in their ads, but this time “The Marlboro Man” was telling his friend “Bob, I’ve got emphysema” and “Bob, I miss my lung.”

So now whenever people see a Marlboro ad, it triggers them to think about the antismoking message. Researchers call this strategy the poison parasite because it slyly injects ‘poison’ (your message) into a rival’s message by making it a trigger for your own.

[key-point]Branding is about connecting deep positive images to your company. But in the future, someone else could “poison” your brand by making the same images a trigger for a negative message. The Marlboro Man can’t be a rugged masculine icon if he has cancer.[/key-point]

6. Strong emotions make us share, like excitement, anger and outrage

getting publicity trump

At his university, Jonah Berger did a big analysis of New York Times articles. Over six months, he recorded which articles made the Most Emailed list on their website. Then he spent weeks scientifically decoding why people shared those articles and not others.

One of his discoveries was:

People are much more likely to email an article to their friend if it arouses strong emotions in them. It actually didn’t matter if the emotions were positive or negative. It only mattered if the emotions were strong or weak.

Articles that made people feel strong positive emotions like amazement, happiness and awe were likely to be shared. Also, articles that made people feel strong negative emotions like anger, outrage or anxiety were also likely shared. But articles that only made people feel weak emotions like contentment or sadness were not often emailed to others.

Scientists can actually measure how strong an emotion you’re feeling is. They call it physiological arousal. In plain English, that means you can feel the emotion strongly inside your body.

So if you are writing an article that you want to be shared you have to ask yourself:

  • Does this article make people’s heart beat faster?
  • Does it make them have butterflies in their stomach?
  • Does it take their breath away?
  • Does it make their blood boil?

Clever politicians have long known that strong emotions inspire people to action. Eric Hoffer studied mass movements like Communism and Nazism. He found that passionate HATE is always used by extremist leaders to give their followers unity and direction. Hoffer said, “Mass movements can spread without belief in a God, but never without belief in a devil.”

[key-point]A strong emotion is something people feel in their body and it inspires action. People need to do something to release that emotional energy. They often release it by talking and sharing.[/key-point]

7. Facts don’t change people, but emotions can

emotions kid running

Do you know how to change someone’s behavior?

For example, if you are the parent of a teenager who is smoking or eating McDonald’s every day, do you know how to make them change? Many parents would get angry. Then they would present all the information about long-term negative effects of smoking. But this approach probably wouldn’t be effective.

The way to change people’s behavior is with emotions, not with information or facts.

Here’s how Jonah explains it:

Most teens don’t smoke because they think it’s good for them. And most people who scarf down a Big Mac and large fries and wash it down with a super sized Coke are not oblivious to the health risks. So additional information probably won’t get them to change their behaviour. They need something more. And that is where emotions comes in. Rather than harping on features or facts, we need to focus on feelings, the underlying emotions that motivate people to action.

Humans are not really rational or logical, even though we often pretend to be. We’re mostly driven by our emotions and then we make up rational explanations to justify our emotions.

For years, governments were telling people how bad smoking is, with little effect. Then they tried other approaches that were more visual and emotional. In many countries, including my country of Canada, the government prints disgusting images on cigarette packs. Images of black lungs or cancer tumors to show what happens if you smoke for 20 years. The disgust starts to become linked with cigarettes in people’s minds, and now people smoke less than ever.

This is a good example of positive propaganda.

Another example…

The New York City health department wanted people to drink less soda. They could have talked about calories and why drinking soda causes obesity, but facts are boring. Teaching facts was not working, so they tried a different approach. They wanted to make people FEEL different about soda.

They created an ad showing a guy literally drinking fat. A big glass of gooey, sticky, lumpy, gross white fat. This disgusting visual image is hard to forget. Next time you pick up a Coke, you may remember this ad and get a water instead. Take a look for yourself:

[key-point]To change someone’s behavior, don’t use rational information or facts. Instead, aim at their emotions. Make people feel something.[/key-point]

8. Public things spread, not private ones

partner couple relationship social connect

The next way to make your idea, product or business more contagious is to make it public. This means your customers should be seen by others using your product. Or if you want to spread an idea or movement, then your supporters need some publicly visible way to show their support.

This is important because humans are social animals. We will naturally copy what we see the people around us doing. Like the old saying goes, “Monkey see, monkey do.”

The more others seem to be doing something, the more likely people are to think that thing is right or normal and what they should be doing as well.

The key is that people need to SEE others using your product. Because if people can’t be SEEN using your product, then others can’t see and copy their behavior. So you need ways to make your product or idea more public and visible, instead of private and hidden. Here are a couple successful examples:

Nike’s Slam Dunk Marketing Strategy

Why do companies like Nike pay athletes millions of dollars to wear their shoes or shirt?

Because millions of people will see an amazing athlete wearing the Nike logo while they are doing athletic feats that look impossible. Slam dunking a basketball. Running faster or longer than anyone ever has before. Hitting a golf ball like a guided missile.

And all the people watching start to believe that if they copy the athlete by wearing Nike shoes, then they might be able to do the same amazing things, too. Nike’s huge growth over the past 20 years is proof this marketing strategy works.

How Hotmail Became Hot

Another great example is Hotmail, one of the first free email services. It was incredibly popular. I remember all my friends using Hotmail many years ago.

Here’s why Hotmail grew so quickly: Every time someone sent an email, at the end of their message you would see the line: “Get your private, free e-mail from Hotmail at” Their website attached this line automatically to any emails sent through Hotmail.

So if you were using Hotmail, all your friends and coworkers would know. And since people naturally imitate what they see others doing, Hotmail grew rapidly. It was a genius way of making their product public.

The iPhone has a similar feature. It automatically adds the line “Sent from my iPhone” to the end of your emails. It’s a great way for the product to advertise itself at no cost.

[key-point]How can using your product become a public experience? How can supporting your idea become something visible and not private? The more people can be SEEN by others using it, the more others can COPY their behavior, and the faster it can spread.[/key-point]

9. Practical value gets shared

skill work effort practice

From his New York Times analysis, Jonah discovered another useful fact. He found that useful articles were 30% more likely to hit the Most Emailed list.

Useful articles that give information that really helps people in a practical way are much more likely to be shared. And that just makes sense. You want to help your friends. If you see an article that can help them, then you may pass it along.

The famous copywriter Gary Bencivenga said the secret to successful advertising is to “Make your advertising itself valuable.” By this, he meant people have been bombarded so much with advertising that they are mostly blind to it. But if your advertising offers some truly vlauable information inside itself, then it will not be ignored. He said, ideally people should find your ad so useful that they cut it out of the newspaper to save it.

In the internet age, this philosophy has transformed into something called content marketing. You publish content that shows people how to do something on your blog, Youtube or podcast. This useful content attracts people that you can later transform into customers.

For example, if you sell a coffee maker, you can make short videos that educate people how to pick great quality coffee beans, how to brew perfect coffee, and how to store their coffee to keep it fresh. People who want great coffee will find your useful content and then you can also introduce them to your coffee maker and educate them why it is better than the competition.

[key-point]People today are bombarded with noisy advertising. To get their attention you need to make your advertising itself valuable. And people are far more likely to share practical and useful knowledge.[/key-point]

10. Stories aren’t just entertainment, they carry information

stories old men riding cart

For a few years, I stopped reading fiction books. Sure, I’d still watch some movies or TV shows, but I figured if I was going to sit down and read, then I should read something that can improve my life and wisdom. So I always read non-fiction books.

Boy, was that a mistake! Because I totally missed the point of fiction.

It’s true that a fictional story does not teach you things like a professor would, but it does teach you important things!

For thousands of years, before humans could read or write, we shared stories. And these stories were not just empty entertainment, they usually carry some important message or idea inside them. Stories are how information, knowledge, and morals were carried down through generations.

For example, I’m sure you’ve heard “The 3 Little Pigs” story before. Three little pigs build three houses. The first two pigs are lazy and they quickly build their houses from straw and wood. A big bad wolf comes and blows their houses down easily.But the third pig slowly and carefully builds his house using bricks.

But the third pig slowly and carefully builds his house using bricks. And when the big bad wolf comes he huffs and puffs, but can’t blow the house down. This is not just a cute story. There’s an important lesson carried inside it. The lesson is that planning and hard work will pay off in the future.

The Subway Guy

Do you remember Subway’s brilliant ad campaign a few years ago?

For years Subway had been trying to brand themselves as “healthy fast food.” They tried talking about the calories in their subs, but like we said before, facts are boring.

Then they found Jared, a guy who lost 245 pounds by eating Subway subs. He had a surprising story that people could easily understand and share. And the “lesson inside his story” was that you could lose weight eating Subway food. It was perfect. Subway’s marketing department spread his story far and wide. It was a huge success.

[key-point]Stories are not empty, they carry things. They carry important lessons or information. What story can you tell to promote your business? Can you share a story of someone reaching their goal with the help of your product?[/key-point]


So the next time you’re about to post on Facebook, Instagram or Twitter, keep these principles in mind. You now know what makes people share. The next step is to really use this information.

  1. First, people talk about things that make them look good to other people. That’s Social Currency.
  2. Second, they talk about what they are thinking of now. And you can make people think about your product or idea more often by designing Triggers.
  3. Third, people share things that arouse strong Emotions in them, both positive and negative.
  4. Fourth, you want people to be Publicly seen using your product or supporting your idea. People will naturally imitate what they see others doing.
  5. Fifth, people like to share Practical Value. How can you give your customers some useful information they will want to share?
  6. Sixth, people share Stories. How can you embed your product’s benefit into a story to make it easily shareable?

If you enjoyed this summary, then pick up a copy of the book because there are a lot more fascinating examples in it.

I also recommend Robert Cialdini’s books or “Made to Stick” by Chip and Dan Heath. They also write about psychology and marketing in a fascinating way that is useful for business.

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