Agreed, a supportive social environment is definitely a good thing. Especially if you surround yourself with peers who think it's normal to do what you're trying to achieve, for example - eat healthily and play sports, or who think rationally and get things done.

I think there's a big difference between "supportive friends" and "a drill-instructor whose job it is to motivate you". I think the latter is purely external motivation, whereas the former lets you set up an environment conducive to intrinsic motivation.