. Why is it that some ideas or behaviors or products start epidemics and others don't? And what can we do to deliberately start and control positive epidemics of our own?. Epidemics are a function of the people who transmit infectious agents, the infectious agent itself, and the environment in which the infectious agent is operating. And when an epidemic tips, when it is jolted out of equilibrium, it tips because something has happened, some change has occurred in one (or two or three) of those areas. The hard part of communication is often figuring out how to make sure a message doesn't go in one ear and out the other. Stickiness means that a message makes an impact. There are relatively simple changes in the presentation and structuring of information that can make a big difference in how much of an impact it makes. It is almost a matter of psychological survival, if one is surrounded and pressed by millions of people, to prevent them from constantly impinging on you, and the only way to do this is to ignore them as often as possible. Indifference to one's neighbor and his troubles is a conditioned reflex in life in New York as it is in other big cities. When people are in a group, in other words, responsibility for acting is diffused. They assume that someone else will make the call, or they assume that because no one else is acting, the apparent problem. Word-of-mouth appeals have become the only kind of persuasion that most of us respond to anymore. We're friends with the people we do things with, as much as we are with the people we resemble. We don't seek out friends, in other words. We associate with the people who occupy the same small, physical spaces that we do. Six degrees of separation doesn't mean that everyone is linked to everyone else in just six steps. It means that a very small number of people are linked to everyone else in a few steps, and the rest of us are linked to the world through those special few. The best way to get in the door is through a personal contact. It isn't just the case that the closer someone is to a Connector, the more powerful or the wealthier or the more opportunities he or she gets. It's also the case that the closer an idea or a product comes to a Connector, the more power and opportunity it has as well. Word of mouth begins when somewhere along that chain, someone tells a person like Roger Horchow. Word-of-mouth epidemics are the work of Connectors. The word Maven comes from the Yiddish, and it means one who accumulates knowledge. A Maven is someone who wants to solve other people's problems, generally by solving his own.. In a social epidemic, Mavens are data banks. They provide the message. Connectors are social glue: they spread it. But there is also a select group of people — Salesmen — with the skills to persuade us when we are unconvinced of what we are hearing, and they are as critical to the tipping of word-of-mouth epidemics as the other two groups. What separates a great salesman from an average one is the number and quality of answers they have to the objections commonly raised by potential clients.