I used to cut myself. Then, one day, I realized that I was the one causing my own pain.
It was so extremely obvious, too. When I was able to see things as they really were and not just how I saw them.
I think maybe that is why so many people have a difficult time understanding why you would do this. The are only able to see it as a way to add pain on top of the pain of the world. They aren't able to see that it is simply a reflection and manifestation of the tremendous pain that you feel. But that is rather understandable because I doubt you even understand why you do it yourself.
Strong emotions manifest themselves in actions, to express how we feel in ways that we cannot do otherwise. It is the way that our subconscious releases those emotions into the world.
Therefore learning to express the way we feel in other ways, more productive ways like arts and hobbies, is generally how we all learn to truly deal with these emotions in a good way, and to become happier in ourselves.
Hopefully you will learn to do this yourself soon.