"You spend your time tweeting, friending, liking, poking, and in the few minutes left, cultivating friends in the flesh. Yet sadly, despite all your efforts, you probably have fewer friends than most of your friends have. But don’t despair — the same is true for almost all of us. Our friends are typically more popular than we are." -- Steven Strogatz
The above was Steven Strogatz's lead-in to his piece on the "friendship paradox" for the NY Times back in 2012:
Presh Talwalkar did a nice treatment of the paradox as well at his blog awhile back:
The friendship paradox was first recorded in 1991 by sociologist Scott L. Feld, demonstrating that most people, on average, have fewer friends than their friends have! It is essentially a result of sampling bias in social networks.
The basic notion can be used to show that, on average, most of your social media contacts as well (Facebook, Twitter, Google+, etc.) have more contacts/followers than you do (assuming your name isn't "Justin Bieber"); or even perhaps (if you care to think about it) that most of your sex partners have had more sex partners than you. In a more serious vein, the paradox has been used to study the course of epidemics, spread through human contact:
“We think this may have significant implications for public health,” said Christakis [Harvard researcher]. “Public health officials often track epidemics by following random samples of people or monitoring people after they get sick. But that approach only provides a snapshot of what’s currently happening. By simply asking members of the random group to name friends, and then tracking and comparing both groups, we can predict epidemics before they strike the population at large. This would allow an earlier, more vigorous, and more effective response.”From HERE.