Obsessive, Determined, Cautious.
I have a few hobbies that I am obsessed with: martial arts, working out, video games. Also, I tend to keep track of how much money I spend, how much I weigh, and how much I eat.
I enjoy the thrill of overcoming a good challenge, whether it's from a tough workout, or from beating (insert hard game) on (insert hardest difficulty). Whether I have to physically exert myself to where my arms feel like jello, or I feel like I'm going to collapse from exhaustion, or whether I have to retry a difficult level on a game 20 times, the victory is all worth it.
I also tend to worry a lot about my future, as well as the aforementioned things that I keep track of. I don't trust people that easily, and I tend to be paranoid at times.