When Jonah Berger was a graduate student at Stanford, in the early aughts, he would make a habit of reading page A2 of the Wall Street Journal
, which included a list of the five most-read and the five most-shared articles of the day. “I’d go down to the library and surreptitiously cut out that page,” he recalls. “I noticed that what was read and what was shared was often different, and I wondered why that would be.” What was it about a piece of content—an article, a picture, a video—that took it from simply interesting to interesting and shareable? What pushes someone not only to read a story but to pass it on?