Contagious

In Contagious: Why Things Catch On, Wharton marketing professor Jonah Berger argues that word-of-mouth spreads not by chance but through six predictable principles he calls STEPPS: Social Currency, Triggers, Emotion, Public, Practical Value, and Stories. The book opens with the story of a $100 cheesesteak from Barclay Prime in Philadelphia, using it to show how remarkable, talkable products gain free visibility. Berger contrasts this with the famous "mystery of the unused blender" — the fact that most word-of-mouth happens offline and about everyday products, not just viral internet sensations. Each chapter develops one principle. Social Currency explains why people share things that make them look smart or in-the-know, citing Please Don't Tell, a New York bar hidden behind a phone booth in a hot dog shop. Triggers shows how environmental cues spark conversation, using the Mars bar and Kit Kat "Coffee" campaign in the 1980s to demonstrate that a product linked to a frequent cue (coffee) gets mentioned more often than a tastier rival. Emotion describes how physiological arousal drives sharing, drawing on Berger's own analysis of the most-emailed New York Times articles. Public discusses behavioral residue and observable behavior, using Livestrong wristbands. Practical Value covers useful content, including the "Six Degrees of Bacon" example. Stories examines narrative transportation, using the Subway Jared ads and the "Man Drinks Fat" viral ad about a man who drank a blenderized Big Mac. Berger supports these frameworks with his own research and others' field experiments, plus extensive data on word-of-mouth. The book, published in 2013, became a New York Times bestseller and is a staple of marketing curricula.