Why people cut: My guess is extremely strong emotions.
Unexplainable intense pain that is overpowering.
Think of a person locked inside a nailed coffin with no way of
escaping. They probably have no idea how to cope and they have no
healthy methods for release.
They think the physical pain from cutting themselves distracts
the emotional torment. Slowly it becomes a habit. Usually
happens to girls because the chromosomes have it that they are more
emotional than guys. But there are probably emotional guys too.
I think everyone has emotions, good and bad ones. Confident
people can be emotionally intense people as well.
Finding the proper channel for release is key. Some people
confide in friends, others play aggressive sports, some will choose
to write or play music, others will let it all out by yelling,
slamming and breaking things. Some play violent computer games to
relief themselves.
I think cutting usually starts in teenage years ba. Growing up
is tough when you are still trying to figure things out. Emotional
literacy is still very raw, with no idea on how to balance or how
to react to the pain.
If you are curious because you know of someone who does it, lend
a listening ear. Offer help. Based on what I know people who cut
themselves are also usually suicidal.
That's why I got my pets, cos they will always make me smile and
love me. 
Nothing else matters anymore when I looked into their eyes.
