In the "two step" model of marketing, well-connected Influentials amplify a trend by relaying media messages out to the social periphery. Marketers can therefore focus on the few as a way of reaching the many.
Watts's theory says the emergence of a trend depends not on Influentials, but on the susceptibility of the public to the "virus." Social-network effects are so complex, he says, that trends are basically random.
A version of this article appeared in the February 2008 issue of Fast Company magazine.