Need help on this psychology case?

There is this case with a man named Harry who abuses himself. The one question I cannot complete on this ignment is why are the restraints (metallic bars that can sometimes prevent self harm) actually reinforcing to Harry. (Instead of making him stop hurting himself it makes him want to hurt himself more). Why does this happen? I need 3 reasons. I think 2 reasons are because it gets him attention and it is a way for him to communicate that he doesn't like a certain situation he is put into, but I need to figure out 1 more reason.