Contagious

Why do certain products, ideas, or behaviors become wildly popular while others fade into obscurity? Why do some stories inspire global sharing, while equally clever ones vanish without a trace? Jonah Berger’s Contagious: Why Things Catch On tackles this mystery, arguing that contagious success isn’t luck or magic—it’s science. Berger contends that word of mouth—not advertising—is the real engine behind popularity. From viral YouTube videos to bestselling products and groundbreaking ideas, people share what they find interesting, emotional, or useful. But, more importantly, certain factors systematically make things more shareable.

According to Berger’s decade of research at the Wharton School, six principles consistently drive contagiousness. He calls them the STEPPS framework: Social Currency, Triggers, Emotion, Public, Practical Value, and Stories. Each principle reveals a psychological trigger that compels people to talk, share, and imitate. In other words, virality isn’t random—it’s engineered by understanding human behavior.

The Power of Word of Mouth

Berger begins by overturning the assumption that expensive advertising causes success. Instead, he shows that word of mouth drives 20–50% of all purchasing decisions. Personal recommendations are more persuasive and more targeted than ads. We trust friends more than billboards, and we tend to pass along information only when we believe someone in our circle will truly benefit. Remarkably, research reveals that only about 7% of word of mouth actually happens online, despite our obsession with social media. Most sharing occurs through everyday, offline conversation at work, over meals, or while standing in line.

This insight matters because it reframes how we think about influence. Berger challenges Malcolm Gladwell’s idea in The Tipping Point that success depends on a few “special” influencers. In Berger’s model, it’s not the messenger who matters most—it’s the message. A truly contagious idea spreads because it’s built for sharing, not just because a celebrity or “maven” endorses it. Think of a great joke—it’s funny no matter who tells it. Similarly, content designed with contagious qualities will spread regardless of who starts the conversation.

From Cheesesteaks to Blenders: Virality Isn’t Luck

Berger illustrates this principle through stories of everyday people who cracked the code of virality—sometimes by accident. Take Howard Wein’s $100 cheesesteak at Barclay Prime in Philadelphia. By transforming a humble street food into a luxury experience, Wein created a dish that wasn’t just a meal—it was a talking point. People discussed it not only because it was delicious, but because it was absurd enough to make them feel “in the know.” Similarly, when Tom Dickson uploaded videos of himself blending golf balls, iPhones, and other improbable items in his Will It Blend? series, he turned a boring product—a blender—into an object of fascination. Both products gained fame not because of massive advertising budgets, but because they sparked curiosity and conversation.

These examples show that even the most mundane products can become remarkable if they invoke the STEPPS. The key is understanding the psychology that makes people share.

The Six STEPPS to Contagious Content

Each of Berger’s six principles acts like a lever that can make ideas spread naturally:

• Social Currency – People share things that make them look smart, cool, or in-the-know. The act of sharing boosts our status.
• Triggers – Environmental cues keep ideas at the forefront of our minds. “Top of mind means tip of tongue.”
• Emotion – When we care, we share. Arousing emotions—whether awe, anger, or humor—drive action more than logic alone.
• Public – The more visible a behavior is, the more likely it is to be imitated. “Built to show, built to grow.”
• Practical Value – People love to share useful information. “News you can use” spreads because it helps others.
• Stories – People think in narratives. Information embedded in stories—like a Trojan horse—travels further and sticks longer.

Berger integrates research and storytelling to bring each principle to life. He connects behavioral science to real-world cases, demonstrating that contagious ideas obey predictable psychological laws. He even measures virality through massive data sets—analyzing thousands of New York Times articles, product reviews, and baby names to reveal consistent patterns.

Why It Matters

In an age overflowing with content, Berger gives you a science-backed playbook for creating ideas that command attention. Whether you’re a marketer, entrepreneur, teacher, or activist, understanding why people talk is a superpower. You don’t need celebrity endorsements or million-dollar ad campaigns. By applying these six principles, anyone can make their product, story, or cause spread naturally—one conversation at a time. As Berger reminds us, it’s not about shouting louder—it’s about designing messages people actually want to share.

Berger begins with Social Currency, the first and most human of the six principles. Simply put, people talk about things that make them look smart, interesting, or “in the know.” Just like we dress to impress, we also share to impress. Each conversation is a subtle performance of identity—what we say reflects who we are.

Finding Inner Remarkability

People don’t spread ordinary stories; they share the extraordinary. Berger calls this inner remarkability—the element that makes something unexpected or “worthy of remark.” He illustrates it through Snapple’s Real Facts—strange trivia printed under bottle caps (“A ball of glass bounces higher than a ball of rubber”). These fun tidbits didn’t cost Snapple anything to print, yet they made customers want to talk about the brand. Similarly, a secret bar in New York City—Please Don’t Tell—used mystery as its marketing strategy. To enter, patrons had to go through a phone booth inside a hot-dog joint. The novelty of finding a hidden cocktail lounge generated massive word of mouth because discovering and retelling the secret made people feel special.

For your own idea, Berger suggests asking: What makes this product remarkable? What’s the story people can’t resist retelling? (Chip and Dan Heath, in Made to Stick, call this “surprising simplicity”—the sticky idea that hooks attention instantly.)

Leveraging Game Mechanics

We’re all motivated by competition and achievement. Berger explains how game mechanics—like frequent flier tiers or Foursquare badges—turn mundane actions into status symbols. On airlines, passengers brag about reaching “Platinum Medallion” or “Premier Executive” status, posting on social media not to share travel tips, but to subtly announce prestige. This visible achievement makes others want the same reward, spreading the brand naturally. Similarly, Burberry’s “Art of the Trench” campaign encouraged customers to post photos wearing Burberry coats. Being featured on the site was social proof of style—and free advertising for the brand.

The Power of Insider Access

Finally, Social Currency thrives on exclusivity. Berger shares how Rue La La transformed a failing discount store (SmartBargains.com) by turning it into an invitation-only fashion club. The same clothes sold like wildfire when framed as elite and limited-time “flash sales.” Making people feel like insiders—knowing a secret, having early access, or discovering a hidden gem—creates irresistible sharing fuel. This is the psychology behind scarcity and status: when access is limited, people assume it’s valuable, and talking about it elevates their own social standing.

“Secret clubs don’t stay secret for long,” Berger quips. The urge to show off insider knowledge guarantees word of mouth.

The lesson? Help people look good by associating your brand or idea with uniqueness, skill, or status. Give them reasons to share—because when they do, they’re not just talking about your product; they’re talking about themselves.

If Social Currency explains why people share, Triggers explains when they share. Triggers are cues in our environment that remind us of related ideas. Berger’s insight here is profoundly simple: the more frequently something is triggered, the more likely it will be talked about.

Why Cheerios Beat Disney

To prove his point, Berger compares Honey Nut Cheerios and Disney World. Although Disney is more exciting, Cheerios generates far more word of mouth. Why? It’s triggered daily at breakfast tables across America. Everyday exposure keeps it top of mind, and that persistent recall transforms an ordinary cereal into a conversation piece. “Top of mind means tip of tongue,” Berger writes—reminding marketers that frequency often outweighs flashiness.

The Power of Contextual Cues

Triggers work because environmental contexts shape thought. Berger illustrates this with a study showing that customers in supermarkets bought more French wine when French music played, and more German wine when German music played. Similarly, he and psychologist Gráinne Fitzsimons helped students eat 25% more fruits and vegetables simply by pairing the slogan “Each and every dining-hall tray needs five fruits and veggies a day” with the visual cue of a cafeteria tray. The trigger—the tray—automatically reminded students of the health message when it mattered most.

You can apply this idea by linking your brand to natural cues in your customer’s environment. Ask: What’s happening around the moment someone might think of you?

Growing the Habitat

Berger calls the network of possible reminders a product’s “habitat.” For example, Kit Kat’s revival campaign linked the candy with coffee breaks (“Kit Kat and coffee: a break’s best friend”). Coffee served as a daily trigger, refreshing awareness multiple times a day. The campaign boosted sales 33% in one year. Similarly, public health teams can “poison the parasite” by using opponents’ triggers. One anti-smoking ad spoofed Marlboro’s cowboy slogans—“Bob, I’ve got emphysema”—so that every Marlboro ad became an unintended trigger for anti-smoking awareness.

Designing for Timing

Not all triggers are equal. The best ones are frequent, relevant, and occur at the right time. Berger notes that Rebecca Black’s “Friday” became a viral hit not because it was good (it wasn’t), but because each Friday acted as a weekly trigger. Conversely, a poorly timed trigger—like reminding people about reusable grocery bags only when they arrive at the store—fails to influence behavior. To make ideas stick, connect them to stimuli that happen where actions do.

The key takeaway: people may forget information, but they rarely forget the environment around them. Context sparks conversation, and frequent, meaningful triggers keep ideas alive long after the initial buzz fades.

Facts inform, but feelings inspire. Berger’s third principle, Emotion, reveals that content provoking intense feelings—especially high arousal emotions like awe, anger, or amusement—spreads faster and farther than neutral information. When we’re emotionally fired up, we’re compelled to act, share, and connect.

The Awe Effect

Berger’s research with The New York Times identified a surprising trend: science articles—like Denise Grady’s piece on photographing coughs with fluid dynamics—were among the most shared. Why would complex, technical stories go viral? Because they inspired awe: a sense of wonder about human discovery. Awe broadens our mental horizons and compels us to share it so others can feel it too. In psychology, Dacher Keltner and Jonathan Haidt describe awe as “a self-transcendent emotion.” Berger reframes it as contagious curiosity—the feeling that moves both heart and mind.

High vs. Low Arousal

Not all emotions drive sharing equally. Sadness, for example, deactivates energy—it makes people reflective, not talkative. But excitement, humor, and anger all elevate physiological arousal—your heart beats faster, your attention sharpens, and you want to do something. Berger proved this experimentally by showing that people who physically jogged in place were twice as likely to share content afterward than those who sat still. The act of arousal—emotional or physical—literally primes us to pass things on.

Stories That Stir

Real-life examples make this vivid. Susan Boyle’s audition on Britain’s Got Talent moved millions because her unexpected voice produced instant awe and joy. Conversely, Dave Carroll’s protest song “United Breaks Guitars” spread outrage and empathy when it exposed United Airlines’ poor customer service. In both cases, intense emotion—not rational argument—drove virality. Likewise, Google’s “Parisian Love” ad sparked global warmth by telling a love story through search queries, transforming a cold product (a search engine) into a vessel of human connection.

Kindle the Fire, Don’t Douse It

If you want your message to move, focus on how it feels, not just what it says. Anger can motivate social justice; humor can lighten and spread awareness; awe can inspire discovery. Berger’s advice echoes the Heath brothers’ “emotional stickiness”—emotion anchors memory. When designing campaigns, choose high-arousal emotions that energize rather than paralyze. As Berger writes, “When we care, we share.”

Whether your goal is marketing a cause or mobilizing a movement, energy fuels engagement. Tap into people’s pulse, and they’ll carry your message further than logic ever could.

People imitate what they see. That’s the essence of Berger’s fourth principle: Public. To spread, behavior must be observable. As he puts it, “Monkey see, monkey do—but only if monkey can see.” When something is visible, it becomes social proof—it signals that it’s normal, desirable, or valuable.

Making the Private Public

Berger recounts how Apple flipped its laptop logo so it would face outward when users opened their MacBooks. By prioritizing onlookers over owners, Apple transformed every coffee shop into an advertisement. The same principle made Hotmail’s automatic email tagline (“Get your free email at Hotmail”) one of the earliest viral campaigns, generating 8.5 million users in a year without paid ads. Actions that advertise themselves create built-in visibility loops. The more people see others using your product or believing your idea, the more it spreads.

Designing for Observability

Berger’s examples show that observability can make or break influence. Students at the University of Arizona overestimated how much their peers supported binge drinking simply because they saw it publicly. By publicizing the truth (“Most students drink four or fewer drinks when they party”), researcher Koreen Johannessen reversed the norm—and reduced dangerous drinking by 30%. The Movember movement applied this visually: men growing moustaches to raise awareness for prostate cancer turned invisible virtue into visible action.

Visibility also explains why Livestrong’s yellow wristbands became a global phenomenon. They served as wearable proof of support and constant reminders of a cause. Their distinctive color, easy wearability, and emotional connection multiplied their spread far beyond Nike’s expectations.

Behavioral Residue

Even after an action ends, traces—what Berger calls behavioral residue—keep influencing others. Buttons, stickers, reusable bags, or online “Likes” leave clues for others to follow. That’s why “I Voted” stickers increase participation: they make invisible civic duty visible. By turning private habits into public symbols, you convert isolated actions into contagious trends.

Berger cautions, however, that publicity can backfire. Anti-drug ads inadvertently suggested that “everyone’s doing it,” normalizing the behavior they meant to prevent. The takeaway: make positive behaviors observable, and keep harmful ones hidden. If something is built to show, it’s built to grow—so show wisely.

We love sharing things that help others. In Berger’s fifth principle, Practical Value, usefulness becomes contagious. When information saves time, money, or effort, it earns the right to be shared. Sharing helpful content makes people feel generous and smart—two powerful motivators.

From Corn Tricks to Coupon Clicks

Take Ken Craig’s viral corn-shucking video. The 86-year-old farmer showed viewers how to microwave corn and slip the cob out silk-free. The simple, practical tip attracted over 5 million views because it solved an everyday problem. Likewise, hikers who discussed vacuum cleaners on a mountain trail remind us that people naturally share useful information everywhere, even outside its context. Berger sums it up: “People talk about what’s useful to them and to others.”

The Psychology of Deals

Berger draws on behavioral economics (from Daniel Kahneman and Richard Thaler) to explain why discounts fascinate us. Value is relative, not absolute. A $100 discount on a grill feels amazing, while saving $10 on a $650 TV doesn’t—though the absolute difference is identical. He calls this the Rule of 100: if the price is under $100, percentages (20% off) seem bigger; if over $100, dollar amounts ($200 off) feel larger. Smart framing amplifies perceived value—and shareability.

Highlighting Value that Matters

Not all deals are created equal. Overuse of “On Sale” signs dilutes impact, but scarcity—“limited time only,” “one per customer”—enhances excitement. Berger shows this through catalog experiments where simply labeling an item as “on sale” increased purchases by 50%, even without changing the price. Humans are wired to signal opportunity and avoid loss. That’s why sharing a good deal feels rewarding—it’s altruism with prestige.

Beyond Bargains

Practical Value is more than discounts—it’s news you can use. Financial firms like Vanguard share helpful investment newsletters because value builds trust. Articles like “Ten Ways to Save Time” proliferate because people love to help their networks. However, Berger warns, utility can also spread misinformation, as with the false vaccine-autism link that went viral for seeming helpful. His advice: verify before you amplify.

Whether sharing a money-saving trick, a life hack, or a smart insight, you build credibility while expanding impact. Helping others spread useful knowledge is the most natural—and ethical—form of contagion.

Berger’s final principle, Stories, captures why information lives longest when wrapped in narrative. Humans are storytelling animals. We don’t just share facts—we share meaning through the stories those facts belong to. The tale of the Trojan Horse illustrates this perfectly: lessons wrapped in drama spread further than warnings stated plainly.

Narratives as Trojan Horses

A story acts like a Trojan Horse: it entertains on the surface but carries your idea inside. Berger shows how Lands’ End’s customer service story—replacing a broken winter coat for free—communicates reliability and warmth far better than any advertisement could. Similarly, the Jared Fogle Subway story, where an obese man lost 245 pounds eating Subway sandwiches, turned a product feature (low-fat food) into an inspirational movement. When stories make your message inseparable from the plot, people can’t tell the story without sharing your brand.

Building Valuable Virality

But not all stories help their creators. Berger contrasts Evian’s “Roller Babies” ad—a viral hit that failed to boost sales—with Panda Cheese’s commercials, where a mischievous panda enforces brand loyalty with humor. The difference? The panda—and the brand—were integral to the joke. As Berger concludes, stories must create “valuable virality.” It's not enough to be shareable; you must be memorable for the right reason.

Embedding the Message

Great stories survive because key details stay constant. Berger references psychologist Gordon Allport’s Telephone Game experiments showing how unimportant facts fade, but central ones endure. When your message is part of the core narrative, it endures retelling. Dove’s “Evolution” video is a textbook example: by dramatizing a model’s transformation through makeup and Photoshop, Dove made its campaign for real beauty both moving and brand-aligned.

Ultimately, stories humanize ideas. Data persuades minds; stories persuade hearts. Berger’s advice: make your idea a story worth telling—and make sure your brand is the hero, not the footnote.