Contagious by Jonah Berger: Summary and Notes

Contagious book summary

“People don’t think in terms of information. They think in terms of narratives. But while people focus on the story itself, information comes along for the ride.”

Rating: 7/10

Related Books: The Hidden Forces That Shape BehaviourThe Psychology of PersuasionTipping Point, The 22 Immutable Laws of Marketing, Hooked

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Contagious by Jonah Berger: Short Summary

Contagious by Jonah Berger explains why things catch on. It answers the question of why some products, services, commercials, and ideas go viral. Some of the reasons explored include word of mouth, practical value, and the power of stories. A good book with lots of practical examples and explanations of viral phenomena.

Why Things Catch On

There are many reasons why things catch on. Some products are just better and others are priced right.

But while pricing, advertising, quality, design, and so on are sound explanations for why things catch on, they can’t explain everything.

Social Transmission

Social transmission or word of mouth significantly determines whether products or behaviors catch on.

Word of mouth is usually more effective than advertising because it’s more persuasive. People are more likely to believe in their friends than in advertisements. Secondly, word of mouth is more targeted as it goes directly to an interested audience.

Conventional wisdom argues that messengers are important for making things go viral. The obvious driver is the message.

There are six principles of contagiousness:

  1. Social currency
  2. Triggers
  3. Emotion
  4. Public
  5. Practical value
  6. Stories

Social Currency

The most powerful marketing is a personal recommendation. We are wired to find pleasure in sharing information with others. People like sharing their experiences with others so much that they can be willing to pay money for them.

Remarkable things provide social currency because people who talk about them appear more remarkable to others. As a result, remarkable things get bought a lot.

“Remarkability explains why people share videos of eight-year-old girls flawlessly reciting rap lyrics and why my aunt forwarded me a story about a coyote who was hit by a car, got stuck in the bumper for six hundred miles, and survived. It even explains why doctors talk about some patients more than others.”

Remarkability can be applied to anything. You can find inner remarkability in a product by thinking about what makes it remarkable.

“Game mechanics are the elements of a game, application, or program—including rules and feedback loops—that make them fun and compelling”

Game mechanics can motivate us at an internal level by encouraging social comparison. People care about their performance in relation to others.

Game mechanics help generate social currency because doing well makes us look good to our peers.

To leverage game mechanics, you need to quantify performance. Help people publicize their achievements.

Another way of generating social currency is to make people feel like insiders.  Use scarcity and exclusivity to make people feel like insiders.


A trigger is an environmental cue that makes people behave in a particular way. Triggers sustain ongoing word of mouth.

An example of a trigger at work happened in 1997 when NASA’s Pathfinder spacecraft landed on Mars. More people bought the Mars chocolate bar because the planet Mars was mentioned more often by news organizations.

Negative feedback can be good publicity as every feedback acts as a trigger that reminds people that your product exists.

“Ducks need water and grasses to eat. Deer thrive in areas that contain open spaces for grazing. Products and ideas also have habitats, or sets of triggers that cause people to think about them. Take hot dogs. Barbecues, summertime, baseball games, and even wiener dogs (dachshunds) are just a few of the triggers that make up the habitat for hot dogs.”


Humans are social animals. Sharing emotions helps us connect.

The feeling of awe drives people to share. Awe is a complex emotion that involves an intense sense of surprise, mystery, and unexpectedness.

Negative emotions like sadness decrease sharing while positive emotions increase sharing. High arousal emotions such as anger and anxiety make people want to share the content more.

“Some products or ideas may seem better suited than others for evoking emotion. It seems easier to get people excited about a new, hip lounge than logistics management. Pets and babies seem to lend themselves to emotional appeals more than banking or nonprofit financial strategy does.”


contagious - public

Making something more visible makes it easier to imitate. One of the key factors to making products catch on is public visibility. If something is built to show, it is built to grow.

People imitate those around them. They do so because other people’s choices provide information and help solve uncertainty. This phenomenon is called social proof.

To make something contagious is to make what is private public.

For example:

Most college students don’t like the binge drinking of their peers. But because their thoughts are private, they can never influence others unless they are made known to everyone.

Practical Value

People like to pass on practical and useful information. Offering practical value makes things contagious because people also want useful information.

“If Social Currency is about information senders and how sharing makes them look, Practical Value is mostly about the information receiver. It’s about saving people time or money, or helping them have good experiences. Sure, sharing useful things benefits the sharer as well. Helping others feels good. It even reflects positively on the sharer, providing a bit of Social Currency. But at its core, sharing practical value is about helping others.”

Some of the things that make practical information worth sharing include:

  • Chance to save money
  • Helping people achieve their goals

How information is packaged also makes it easier to share. The audience also determines whether or not a piece of information is going to be shared.


People don’t think in terms of information. They think in terms of narratives. Stories make it easier to share information. They even make lessons more relatable.

“Narratives are inherently more engrossing than basic facts. They have a beginning, middle, and end. If people get sucked in early, they’ll stay for the conclusion.”

Stories allow us to learn from the world. They distill the rules and the standards of society.

“Virality is most valuable when the brand or product benefit is integral to the story. When it’s woven so deeply into the narrative that people can’t tell the story without mentioning it.”