I'm ADD, depressive, suffer from bouts of extreme anxiety, and antisocial to top it all off. I have never tried to commit suicide, and I usually
don't purposefully harm myself (except for body art). Doesn't mean that I can't simpathize with someone who does inflict bodily harm upon
themselves. Thing is that I've been forced to deal with it by myself. When I realized that noone was gonna help me and all the kids that used to pick
on me wouldn't be bugged at all if I was gone, I decided that I was gonna get back at all the people that made me upset by living so I could torment
their arses.

That's just me, though.
The best way I can think of to describe why (some)one would hurt themselves over stuff is this: When you get mad and frustrated, what is the most
common reaction? Something violent. Punch the wall, puch out whoever pissed you off, etc. Well, some people feel abandoned by the world and are
frustrated, angry, whatever. They want to break something, so they 'break' themselves. Sometimes, if they feel like they are being a burden and
useless to society and noone wants them, they try to actually kill themselves.
Parhessia actually put it into reasonable terms:
It can be a release of pain felt inside. A transfer of the inner pain to actual physical pain that can offer some sort of relief to the person
doing it, because nothing else may offer such a relief.
Sad thing is that when you feel abandoned by the world, you are blind to help. When someone tries to give you a hug when you are depressed (not just
'blue') and tell you you are a good person, alot of the time you will feel like they are just patronizing you, or even making fun at you. It seems
like everything good that happens to you is just there to prolong the pain. So it will feel good to feel physical pain. The physical pain temprarily
overwrites the pain you feel inside.
Sometimes people self-mutilate.
Sometimes people turn to drugs.
Sometimes people hurt other people.
Me? I break stuff.