Contagious: Why Things Catch On

In Contagious: Why Things Catch On, marketing professor Jonah Berger unveils the science behind why products, ideas, and behaviors become popular. Drawing from his research at the Wharton School, Berger identifies six key principles that make things contagious and explains how anyone can apply these insights to make their messages, products, and ideas spread.

The Central Premise: Understanding Social Transmission

Berger’s core argument is that word-of-mouth and social influence are the primary drivers of popularity. His research shows that:

• Word-of-mouth generates more than twice the sales of traditional advertising
• People are 70% more likely to try something recommended by a friend
• Social transmission is the reason why some products become hits while others flop

Rather than relying on expensive advertising campaigns, Berger shows how understanding the psychology of sharing can make anything contagious.

The Six Principles of Contagiousness (STEPPS)

Berger distills his research into six principles that make products and ideas spread: STEPPS

1. Social Currency (Social Currency)

People share things that make them look good. When sharing makes people feel special, knowledgeable, or part of an exclusive group, they’re more likely to pass information along.

• Examples: Exclusive experiences, insider knowledge, remarkable achievements
• Application: Make people feel like insiders or experts when they share your product or idea

2. Triggers (Triggers)

Environmental cues that remind people of your product or idea increase the likelihood they’ll talk about it.

• Examples: Peanut butter and jelly, Kit Kat and coffee, Rebecca Black’s “Friday”
• Application: Design products and messages that are triggered by frequent environmental cues

3. Emotion (Emotion)

When people care, they share. Content that evokes high-arousal emotions (both positive and negative) is more likely to be shared.

• Examples: Inspiring stories, funny videos, outrageous news
• Application: Focus on evoking emotions that activate people and prepare them to act

4. Public (Public)

The more public and observable something is, the more likely it is to be imitated. People follow the lead of others, especially in uncertain situations.

• Examples: Livestrong bracelets, luxury cars, visible logos
• Application: Make the private public so people can see what others are doing

5. Practical Value (Practical Value)

People like to help others, so they share content that they think will be useful to friends and family.

• Examples: Life hacks, deals and discounts, how-to guides
• Application: Package information in ways that make it seem helpful and valuable

6. Stories (Stories)

Information travels in the form of narratives. People don’t just share facts; they share stories that contain information.

• Examples: Subway sandwich story, Dove Evolution, customer testimonials
• Application: Embed your message in a story so that people can’t tell the story without telling your message

Real-World Applications

Berger illustrates each principle with compelling real-world examples:

Social Currency

• The Economist’ famous subscription offer that included an expensive iPad option primarily to make the print + digital subscription seem reasonable
• Blendtec’s “Will It Blend?” campaign that made viewers feel like insiders in on the joke

Triggers

• Mars’ sales spike when the Mars Rover was in the news
• Rebecca Black’s song “Friday” that became associated with the day of the week

Emotion

• The “Share a Coke” campaign that evoked happiness and connection
• The ALS Ice Bucket Challenge that combined fun with a serious cause

Public

• The yellow Livestrong bracelets that made support for cancer survivors visible
• Tesla’s distinctive car designs that make ownership obvious

Practical Value

• Google’s Gmail that offered more storage space than competitors
• Groupon’s deals that provided clear value to customers

Stories

• The story of a Blendtec blender that could blend an iPhone
• Dove’s “Evolution” video that told a story about beauty standards

Part I: The Science of Sharing

Understanding Word-of-Mouth

Berger explains why word-of-mouth is more effective than advertising:

• It’s more persuasive because it comes from trusted sources
• It’s more targeted because people share with relevant others
• It’s more timely because it happens when people are talking about products or ideas

The Role of Social Influence

Berger shows how social influence affects behavior in ways people don’t realize:

• People are affected by others even when they don’t know them
• Social influence is more powerful than direct persuasion
• People often don’t recognize when they’re being influenced

Part II: Making Things Contagious

Designing for Sharing

Berger provides practical guidance for making products and ideas more shareable:

• Incorporating the six STEPPS principles from the beginning
• Understanding the psychology behind why people share
• Creating experiences that people want to talk about

Measuring Contagiousness

Berger introduces methods for evaluating how contagious a product or idea might be:

• Assessing which of the six principles are incorporated
• Testing how likely people are to share
• Tracking word-of-mouth and social transmission

Key Concepts and Principles

The Power of Word-of-Mouth

Berger emphasizes that word-of-mouth is the primary factor behind:

• 20-50% of all purchasing decisions
• The success of many viral marketing campaigns
• The spread of social movements and ideas

The Psychology of Sharing

Berger identifies several psychological factors that drive sharing:

• The need to inform and help others
• The desire to reinforce identity and values
• The urge to bond with others through shared experiences

The Importance of Design

Rather than relying on luck or expensive advertising, Berger shows how contagiousness can be designed into products and messages from the beginning.

Practical Applications

For Marketers and Businesses

• Design products and campaigns that incorporate the six STEPPS principles
• Focus on word-of-mouth rather than traditional advertising
• Create experiences that people want to talk about

For Entrepreneurs and Startups

• Build contagiousness into products from the beginning
• Leverage social transmission to grow without expensive marketing
• Understand why some startups succeed while others fail

For Non-Profit Organizations

• Use the principles to spread awareness of social causes
• Create campaigns that people want to share
• Make messages more likely to go viral

For Anyone with an Idea

• Apply the principles to make ideas more shareable
• Understand why some ideas spread while others don’t
• Increase the chances that ideas will catch on

The Impact of “Contagious”

Since its publication in 2013, Contagious has had significant impact:

• It’s become required reading in marketing and business programs
• Companies worldwide have applied its principles to their products and campaigns
• It’s been translated into over 30 languages
• It’s influenced how people think about viral marketing and social media

Criticisms and Considerations

While widely praised, Berger’s approach has faced some criticism:

• Some argue that not all products can be made contagious using these principles
• Others question whether the principles apply equally across all cultures
• The focus on manipulation raises ethical questions about influencing behavior

Conclusion

Contagious provides a powerful framework for understanding why things catch on. Berger’s insights help readers:

• Understand the science behind word-of-mouth and social transmission
• Recognize the six principles that make products and ideas spread
• Apply these principles to make their own messages more contagious

The book’s enduring popularity reflects a widespread need to understand how ideas spread in our hyperconnected world. Berger’s research-based approach and practical examples make complex concepts accessible and actionable.

Whether you’re a marketer trying to make a product successful, an entrepreneur launching a startup, a non-profit trying to spread awareness, or anyone with an idea they want to share, Contagious provides valuable tools for making your message spread.

Berger’s central message is empowering: virality isn’t random luck but a science that can be understood and applied. By incorporating the six STEPPS principles into products and messages, anyone can increase the chances that their ideas will catch on.

The book ultimately encourages readers to think more strategically about how information spreads and to design products and ideas that people actually want to talk about.