From my experience, I can say that whether I do things I want to do (and which ones) depends largely on the environment.

In summer of 2007 I got up at 5 AM and jogged because I read an article describing the benefits of rising early and upon trying it out discovered that I like witnessing the sunrise. As autumn came it became increasingly difficult to get up in darkness until I stopped. Last summer I thought wanted to lift weights but I didn't do anything. This year I read Playing to Win and saw a friend of mine who has been exercising for a year; and now I'm going to the gym three times a week.

So why am I not doing this or that? Because my external world lacks enough stuff that would change the default action from do-nothing to something else.