Because they are angry at the world and themselves. And mostly at themselves for always screwing up, but if they took it out on someone else the would jyst be screwing up again. When the harm themselves, not only are they releasing all of that anger, but they are repremendimg themselves and therefore feeling like this will help them be better. What they need is love and to understand that they are lived and to feel included.
Why do people hurt themselves?
by Isuck_anyway July 9, 2018