There's fascinating research coming out now about the value of your social network. In the book Connected, it talks about how your behaviour subconsciously influences your friends, their friends, and their friends' friends.
Mirror neurons. Emotional contagion. A lot of scientific phenomenon speaks to this. The people you surround yourself with dramatically influence your beliefs, because their thinking is like a mind virus, and beliefs are contagious. Your social network and the way your friends behave influence your behavior and habits. If you hang around with marathoners, there’s a much greater chance you’re going to get fit. Let's explore...

"Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives."
https://www.amazon.com/Connected-Surprising-Networks-Friends-Everything/dp/0316036137