It's true that nothing but personal experience can allow you full understanding. I think if you turn that on its head you can also find some truth from the perspective of someone on the inside. Yes, people who have never hurt themselves on purpose can't understand the motivation behind our way to cope, but those who do self harm can't comprehend why everyone else thinks it's so horrible. Personally, I know on a rational level that self harm is not healthy or something to be proud of. However my rational mind has never been the one at work when I start to look for a blade. When you're in a world you don't recognize and are afraid that nothing is real anymore, when the smallest thing causes an emotional response and your body aches in anticipation, when you need to stop feeling because you can't release everything inside you, or when you need to feel pain because you are a horrible person and deserve it, then maybe you can understand why the price of physical pain seems so small. Of course once your secret is out there, when people start to notice that certain parts of your body are always covered, or wonder what caused every injury no matter how innocent it looks -- you are no longer permitted to complain. If you have pain, even if it is unrelated to self harm you are not given the sympathy everyone else gets. Stubbed your toe? Don't complain because everyone has that instant thought pop into their mind:
"Why is she complaining? Doesn't she like pain, isn't that what she wants?"
That's where the false assumptions come in. I don't seek out physical harm at every hour of the day, if someone throws a ball at my head I am still going to have the natural response of protecting myself. It's difficult to explain, go figure, but sometimes any old injury isn't enough. You have to be the one in control because that's what drives your need to self harm in the first place -- control, and the feeling that you lack it. Life is chaos, self harm is my organization. It's also my protection, if I can cut into my own flesh then I am confirming to myself that I can handle any pain that is thrown at me. If others know I self harm maybe they will stay away from me, be afraid that I am unstable or maybe just not want to touch me where I've self harmed. That way I can stay isolated and the only thing that can hurt me is myself.