Nicholas Christakis and James Fowler (2009), pioneers in research on social networks, report that attitudes, behaviors, and habits move through social networks via the three degrees rule. For instance, your behavior (say, your food preferences) can affect your friends (one degree) and their friends (two degrees) and their friends' friends (three degrees). So we are influenced by and influence our friends within three degrees of separation, but not much beyond that (Christakis & Fowler, 2009).