Friends of Friends

Once you understand the logic of how other people affect us, say Nicholas Christakis and James Fowler, authors of Connected, then you understand that if you hope to change yourself, you better try to change not just your friends, but your friends' friends, too:

At both the individual and the population levels, it is more effective for you to lose weight with friends of friends than with friends. The problem is this: If you attempt to lose weight with your friends, you might succeed, but this tiny cluster of you and your friends is surrounded by a large group of people exerting pressure to gain weight again. In all likelihood, both you and your friends will thus regain weight.

The authors go onto suggest that a good strategy to lose weight, therefore, would be to create a running club of friends-of-friends, thereby creating a buffer of healthy people around you.