There are a few reasons why people do it. I don't want to sit here and type out reasons that you may translate as reasons for you to do it. For me, it started with curiosity... just so happens that I wasn't all that stable at the time, and it ended up turning into something darker. (4 years clean, now) If you're considering it, ... don't.

It's a release you can pretty much get from doing other things. Endorphins and adrenaline; that's sometimes all there is to it, at least physically. Not worth it, trust me on that much, please. |: I'd rather eat a chocolate bar, workout, or cry, than ever go back to that dark time. :\ And I hate crying! xD

I don't mean to demean how horrible it is, or anything like that; I'm not really the person to do that, it's just that I know... I struggle to explain this, and I know I wouldn't even listen if I went back in time. I was so stubborn, typically. I call it "fog" (as do some others, I believe) It stops you seeing things for what they are... makes you interested in one thing... so much like an actual drug, it's scary. Being on the other end (girlfriend who was very unstable) was a huge eye-opener for me, as well. It's not just about what one does to oneself, but the effect it has on others.