Contagious: Why Things Catch On

Berger's central claim is that social epidemics are driven by the characteristics of messages and ideas themselves, not by the special people who transmit them. The book explicitly rejects Malcolm Gladwell's Tipping Point thesis that a small number of mavens, connectors, and salesmen drive virality. Where Gladwell focused on the 'who,' Berger focuses on the 'why.' He argues that if you understand the six STEPPS principles—Social Currency, Triggers, Emotion, Public, Practical Value, and Stories—you can design content that people will share, regardless of who initially spreads it. This reframing makes virality a property of the message, not the messenger.

The book introduced the STEPPS framework: Social Currency (sharing things that make us look good), Triggers (environmental cues that remind us of a product), Emotion (high-arousal feelings drive sharing), Public (visible behaviors imitate more easily), Practical Value (useful information gets passed along), and Stories (narratives carry ideas). Each principle addresses a different psychological mechanism behind sharing. For example, Triggers explains why Mars bars sold more during NASA's Mars missions, and Emotion explains why Susan Boyle's audition and 'United Breaks Guitars' both went viral despite opposite emotional valences—anger and awe are both high-arousal.

Gladwell's Tipping Point argues that social epidemics spread through the efforts of three special personality types: mavens (knowledge accumulators), connectors (social hubs), and salesmen (persuaders). Berger directly challenges this. He contends that the message matters more than the messenger. In his account, Gladwell overemphasized individual influence and underemphasized the structural features that make some ideas inherently more shareable than others. The Boston Globe review noted that Berger 'points out' conventional wisdom is wrong, and the Christian Science Monitor framed the distinction as Gladwell writing about the 'who' while Berger writes about the 'why.'

Berger reports that word of mouth drives 20 to 50 percent of all purchasing decisions, making it more influential than traditional advertising. Crucially, he found that only 7 percent of this conversation happens online—the vast majority is face-to-face. This finding challenges the assumption that digital platforms are the primary vector for social transmission. It also explains why the STEPPS framework emphasizes triggers and public visibility: everyday environments and observable behaviors generate far more conversation than a single viral post, because they operate continuously rather than in isolated bursts.

A frequent oversimplification treats STEPPS as a checklist where loading a message with all six principles guarantees virality. Berger's framework is diagnostic, not formulaic: different messages benefit from different principles, and the principles can sometimes conflict. The book itself contains cautionary examples, such as anti-drug campaigns that backfired by making drug use seem more prevalent, illustrating the 'Public' principle working against the campaign's goal. The Boston Globe review questioned whether Berger's confident claim that 'anyone can use' STEPPS to make 'any product or idea contagious' overstated the framework's reliability.