When it comes to epidemics, not everyone is created equal. Some people, because of their particular social gifts, are much more important than everyone else in determining whether an idea or behavior or product will catch on. Paul Revere, with his incredibly wide and varied network of acquaintances, is the classic example of a Connector. When a Connector gets interested in an idea or a type of salad dressing, a lot of people will hear about it in passing. Mavens may not know a lot of people, but they know a particular subject deeply and feel compelled to pass along this information.
Salesmen are persuaders.
Sometimes just the smallest of shifts can mean the difference between success and failure. Take Big Bird. In 1969, Sesame Street was a couple of months short of going on the air, and producers tested the show on preschoolers in Philadelphia. The kids loved the Muppets, but got quickly bored when the scene shifted to Sesame Street itself. The kids didn't find it interesting to watch the adults and children there talking and doing things together.