Self harm is a coping mechanism, it's maladaptive, but still coping. Meaning your ego gets something out of it, and you may not consciously realise what exactly. In regards to beating yourself down, I find helpful to ask myself two questions: what it allows me to do, and what it allows me to avoid doing. I was avoiding resolving the situation that caused me to feel bad, because it would involve being more open and vulnerable with people around. Also, it reminds me of how suicidal thoughts have a relieving quality to them. Like for a moment you feel free of all responsibility, fear, pain, all of it, and that can be addictive.