Nicholas A. Christakis says,

We found that weight gain in a variety of kinds of people you might know affected your weight gain — weight gain in your friends, in your spouse, in your siblings and so forth. Moreover, people beyond those to whom you were directly tied also influenced your weight, people up to three degrees removed from you in the network. And, incidentally, we found that weight loss obeys the same properties and spreads similarly through the network.

Who cares whether or not Mike Moffatt achieves his weight loss objective?

Maybe you should care. He’s might be within three degrees of separation from you.

Christakis continues,

In our empirical work so far, we have found substantial evidence for the latter mechanism, the spread of norms, more than the spread of behaviors. It is a bit technical, but I will tell you why we have some evidence for norms. In our empirical work on obesity, we found two lines of suggestive evidence for a spread of norms. The first line of evidence caught everyone’s attention, and frankly it caught our attention when we noted it. It showed that it did not matter how far away your social contacts were; if they gained weight, it caused you to gain weight. This was the case whether your friend lived next door, ten miles away, 100 miles away, or 1000 miles away. Geographic distance did not mater to the obesity effect, the interpersonal effect.

Social norms. Wasn’t I just talking about social norms?