Summary of Contagious by Jonah Berger

  • Post category:Summaries
  • Post last modified:September 18, 2023

Summary: 8 min

Book reading time: 4h47

Score: 7/10

Book published in: 2013

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  • Word of mouth is the best marketing strategy by far.
  • Messages that spread through word of mouth are valuable and wrapped in stories.

Table of Contents

What Contagious Talks About

Contagious: Why Things Catch On is a book written by Wharton marketing professor Jonah Berger. It’s a roadmap to create stories and messages that spread fast. It also explains what makes a post, video, or picture go viral on the Internet. The book taught me that word-of-mouth happens when a message is worth sharing.

While the beginning of Contagious is informative, 2/3 of the book are useless.

Berger uses too many examples to highlight his principles. I felt he was doing so because he had nothing else to say.

The information in the book is great for writers and marketers, but no need to read the book. This summary will suffice.


If you still want to buy the book, you can do so here.

Summary of Contagious by Jonah Berger

Why do certain ideas and products propagate and sell, while others don’t?

Possible reasons:

  • performance
  • price
  • marketing
  • word-of-mouth (WOM), also called social influence.

WOM helps restaurants make $200 more per customer. A 5-star review on Amazon sells 20 more books. And doctors are more likely to prescribe drugs other doctors have prescribed.

WOM massively influences. It is more effective than advertising because it’s more trustworthy: you trust your friends but have a hard time trusting ads.

It is also more targeted.

If you tell a friend about your will to try a vegan restaurant and that friend tells you which one to go to, chances are you will go to that one exactly.

The “ad” happened at the right time at the right place with the right person.

Finally, WOM is available to everyone. The only question is: how can marketers get it started?

How do you focus on the people that need what you have, and how do you make sure WOM propagates?

If you are thinking “just go online”, be aware that only 7% only of total WOM happens online (at least when the book was written in 2016, I don’t know about now).

If you want your message to go viral, you need to craft it according to the 6 principles of virality.

Principle 1: Social Currency

We want to look cool, good, rich, smart, fun, and influential. As such, design a product, service, or message that will make people cool when they tell about it to their friends.

Principle 2: Triggers

When you think dog, you also think cat. Dog is a trigger for cats.

You need to design a product that is frequently triggered by the environment. You can also create new triggers by linking your products and ideas to already-existing cues in that environment.

Principle 3: Emotion

Your idea must evoke emotions. When people feel something, they share it with others. Instead of focusing on function, focus on feelings.

Principle 4: Public

Make your product seen, make it public. Humans interact in large paths by copying each other’s behavior.

Principle 5: Practical Value

Create ideas that are useful. Useful means saving time, money, or effort. Highlight the incredible value of your product, and make it as easy to share as possible.

Principle 6: Stories

Wrap your message in a story.

Together, these principles can be contracted into STEPPS.

Think of them as the 6 STEPPS.

Principle 1: Social Currency

In NYC, there is a secret restaurant hidden inside a hot-dog restaurant inside.

That bar, called Please Don’t Tell, has been one of the most sought-after bars in New York ever since it opened.

It never advertised.

It worked because the bar is based on the idea that it’s a secret. If it’s a secret, it is valuable. If it’s valuable, you want to share it with others as it will enable you to look better in their eyes (you’re the guy that knows about valuable stuff).

Sharing is in our genes. When kids complete a project, the first thing they do is show others. They want social validation regarding what they have designed.

We do too, which is why we are talking so much about ourselves (roughly 40% of the time).

The remaining 60% is valuable content to be seen positively in the eyes of others – such as sharing secrets.

Something becomes remarkable when it is unusual, extraordinary, or worthy of notice or attention.

The brand Snapple inserted random facts under the cap of their soda bottles. The facts were so random and remarkable that they spurred the sharing of these facts right away – hence sharing the brand.

Another way to get your product talked about is to make a game out of it.

One builds a game when one measures performance (miles from airlines).

Another way to build games is to get people to participate in a contest. Burberry built a website with stars and random people wearing Burberry clothes. The random people had to send their pics to Burberry. The website drove sales by 50%.

You can also organize a contest that demands the support of the population so candidates can win. Candidates will talk about you by rallying people around them.

Finally, the last way to generate social currency is to make people feel like insiders.

One way it was applied was by Smartbargains which created Rue La La. Rue La La sold the exact same items as Smartbargains, but consumers had to register to the site and the sale would last only 24 hours maximum.

It made people feel like insiders.

You do so by engineering scarcity and exclusivity.

Scarce things are less available hence more valuable. Exclusivity entails that it is available only to people meeting certain criteria.

If people get something they are alone to own, it makes them feel special and unique. They will tell others about it.

When McDonald’s introduced the McRib, it didn’t work. So they decided to make it scarce. It would come back once in a while, and only in certain locations. People started demanding that McDonald’s “bring back the McRib.”

Principle 2: Triggers

There are two types of WOM. Immediate WOM (“I got the new iPhone!”) and ongoing WOM (“actually, those pants are really comfortable”).

The difference between the two is trigger. Triggers are reminders spread in the environment. The smell of waffles can remind you to buy waffles on your way home.

Seeing a dog in the park can remind you you have always wanted one.

In 1992, Mars sales increased unexpectedly. The reason was that NASA was preparing for a mission…to Mars.

Triggers matter to the extent that if people vote in a church, they will be more sensitive to religious matters like abortions, while if they vote in a school, they will be more sensitive to policies favoring education.

Triggers influence WOM. When Geico made an ad with a caveman saying that switching to Geico was so easy “even a caveman could do it”, it bombed. No one sees cavemen around anymore.

But when Budweiser associated the word “wassup” with beer, sales took off.

When Kit Kat sales slump in 2005, the marketing team found out people ate Kit Kat during a break or with their coffee. They launched ads associating Kit Kat to coffee and it was a huge success.

The effectiveness of triggers depends on several criteria.

  1. Frequency: the more often the trigger is received, the stronger it will be. When an ad for a bathmat featured a guy dying when getting out of the shower, it bombed. You can’t buy bathmats when you are taking a shower.
  2. The context is another one. Russians see more snow than the Spanish do. Similarly, products associated with the color orange sell more around Halloween than they do the rest of the year.

Sometimes, bad publicity can help sales if the publicity is a trigger putting the product at the top of the mind.

Principle 3: Emotions

Emotions that spur sharing are arousing emotions.

According to Wikipedia, arousal is “the physiological and psychological state of being awoken or of sense organs stimulated to a point of perception.”

These are awe, anger, anxiety, etc.

When we say arousal, we often think of sex, but arousal isn’t only about sex. It’s any state that reinforces our perception. And anger, anxiety, and fear are arousing emotions.

Arousal triggers action, so, arousal helps to share.

Sadness, for example, is not arousing. Sadness stifles action.

As such, when crafting your message, don’t make the content a priority. Make the feeling it triggers a priority.

Example from Google.

To find the underlying emotion, the author suggests using the three “why’s”. Why do people use the product? Why? And why? This is the underlying emotion.

Emotional arousal is not the only arousal that compels people to share. Physical arousal too.

For example, you will be more likely to share an article or an idea or to take action in general, after jogging than after relaxing in your chair for 20 minutes.

Arousal, be it emotional or physical, triggers action. In fact, arousal may trigger you to share too much information.

Finally, people don’t want to be told something.

They want to be entertained. They want to be moved.

Principle 4: Public

If something is built to show, it’s built to grow.

This is why everyone goes to the restaurant where everyone goes and why no one goes where no one goes.

This is why students binge drink, even though most of them are uncomfortable doing it.

This is why everyone buys the same shirt, but not the same socks.

In fact, warm cities where people are outside often have people copying each other more than cold cities.

The easier something is to see, the more people talk about it.

The main idea of this section is that if people cannot see what others do, they won’t copy the behavior.

As such, whatever the private part of what you sell is, make it public!

While most products will be adopted by people watching other people adopting them, some products will be adopted after.

When it happens, it is called behavioral residue.

When Lance Armstrong created the Livestrong foundation, they sold yellow bracelets to raise money. The bracelets left traces of the Tour de France.

It’s the same principle as the “I Voted” sticker.

This principle is also dangerous to use in the case of anti-behavioral ads. When the “Just say no” anti-drug campaign came out in the US in the 1980s, people that had seen the ad were more likely to take drugs because it made drug consumption more public.

Principle 5: Practical Value

When you see something that could be valuable to somebody, you share it with them because helping somebody helps you bond with them.

So, how do you make something valuable?

Value = saving time, money, and efforts.

However, it depends on how you present it.

People are more likely to buy at 250 if they can save 100 than to buy at 240 if they’re only saving 15.

350 250 > 255 240

They are also more likely to make efforts to acquire something for 15 instead of 25 than for 640 instead of 650 (while in both cases, they save 10).

This principle is called diminishing sensitivity. Earning 20 instead of 10 feels MUCH BETTER than earning 1020 instead of 1010.

This also means that it is better to advertise 200 off a 2000 price than 10% off. Likewise, it’s better to advertise 10% off on 20 than 2 off.

Principle 6: Stories

Stories are the original form of entertainment. This is why we are so fascinated by it. It’s also a way to learn lessons.

“Work hard” will not leave any traces. But the story of the three little pigs will.

Stories are an important source of cultural learning that helps us make sense of the world. They give people the information they need in a way that is easy to remember.

People are also less likely to argue against stories than against advertising claims.

The way to use stories for virality is to take a product and build a story around it. But the story must be about your product. You can’t have a guy in an airplane talking about the best brand of timber!

That is what happened with Evian’s baby dancing ads. Everyone saw the ad, but Evian’s market share didn’t budge. Dancing babies weren’t related to water.

You need to make the benefit of your product a key part of the narrative. 70% of details are lost when people tell a story they heard. Make sure your message is in the 30%.

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