My daughter has a friend who has cycled through various sorts of selfdestructive behavior. For this young woman it is, I think, a way to convince herself that she is as unimportant and she thinks her parents and friends think she is. They don't notice the cutting, because they don't notice her, and this is how she proved it. (This is a rough translation of what I understand is her take on it--I've read some of her poetry on her blog and posted supportive remarks after some of them.)

I think she has grown out of some of that in the last year or two.

SRS