Contagious: Why Things Catch On

Reviewed by Diario de un Inversor · UpdatedJuly 8, 2026

Our review

Jonah Berger is a marketing professor at Wharton who spent a decade on one concrete question: why do some ideas, products and behaviours spread while others, apparently better, do not? His answer is organised into six factors summarised by the acronym STEPPS: social currency, triggers, emotion, public visibility, practical value and stories. The book's strength is that it does not merely describe viral cases after the fact — the genre's habitual vice — but draws on controlled experiments (which headlines get shared more, which emotions drive transmission and which inhibit it, how physical context triggers recall of a brand) and sets out the methodology. Berger is honest about the limits: he identifies observed regularities, not a reproducible recipe, and warns that most deliberate attempts at virality fail. For anyone analysing companies, the interest lies in understanding why word of mouth is simultaneously cheaper and more credible than paid advertising, and why that advantage cannot be bought: it is built from the product.

Key takeaways

• The STEPPS framework gathers six factors that favour the social transmission of an idea.
• Berger draws on controlled experiments, not only retrospective analysis of viral cases.
• Word of mouth is more credible and cheaper than paid advertising, but it cannot be bought.
• The author himself warns that he describes observed correlations, not a reproducible recipe.

Fact

Berger is a marketing professor at the Wharton School; the book was published in 2013 and its framework is summarised by the STEPPS acronym.