Researcher Robert Cialdini once demonstrated with a fascinating experiment the persuasive power of desiring the possessions or experiences of others. Several hundred volunteers took their seats in a room, purportedly to fill out a survey. But that was only a distraction from the real purpose of the experiment, which had to do with how our behavior is swayed by those around us. A large glass jar of cookies stood prominently on a nearby desk.

"Would you like a cookie?" one of the researchers asked the survey takers. Approximately one fifth of the volunteers took him up on his offer. In the second stage of the experiment, the research team secretly removed most of the cookies from the jar, so that it looked as though others had already taken one. Still, only about one fifth of respondents reached for a cookie.

In the final stage of the experiment, however, a researcher sat behind a desk beside a large glass cookie jar. But this time, before the researcher could ask volunteers if they wanted a cookie or not, a stranger ambled into the room, removed the glass lid, took a cookie in front of everyone in the room, and walked out again. This time, when the survey takers were asked if anyone wanted a cookie, nearly every single person took one.

This experiment suggests something that advertisers and marketers have long been instinctively aware of: humans want what other humans want. And the more visible other people's demand is, the more we want what they are having. In the cookie jar experiment, people didn't want more cookies when they thought that others might have taken a cookie. But when they actually saw another person take a cookie, their brains said, Gimme!