What must underlie successful epidemics, in the end, is a bedrock belief that change is possible, that people can radically transform their behavior or beliefs in the face of the right kind of impetus. This, too, contradicts some of the most ingrained assumptions we hold about ourselves and each other. We like to think of ourselves as autonomous and inner-directed, that who we are and how we act is something permanently set by our genes and our temperament. But if you add up the examples of Salesmen and Connectors, of Paul Revere's ride and Blue's Clues, and the Rule of 150 and the New York subway cleanup and the Fundamental Attribution Error, they amount to a very different conclusion about what it means to be human. We are actually powerfully influenced by our surroundings, our immediate context, and the personalities of those around us. Taking the graffiti off the walls of New York's subways turned New Yorkers into better citizens. Telling seminarians to hurry turned them into bad citizens. The suicide of a charismatic young Micronesian set off an epidemic of suicides that lasted for a decade. Putting a little gold box in the corner of a Columbia Record Club advertisement suddenly made record buying by mail seem irresistible. To look closely at complex behaviors like smoking or suicide or crime is to appreciate how suggestible we are in the face of what we see and hear, and how acutely sensitive we are to even the smallest details of everyday life. That's why social change is so volatile and so often inexplicable, because it is the nature of all of us to be volatile and inexplicable.