I do it because the pain enhances my orgasm, up to the point, which is highly variable, even with the same torture, where the pain in my sexually excited state truly becomes unbearable. At which point, I lose my desire for an orgasm--the mechanism in my brain to stop the pain takes over. If I can come just before that happens, two things happen--a mind-numbing orgasm, followed by real AGONY! Obviously the orgasms are worth it, and addicting BTW, otherwise I would have stopped such "insane" behavior long ago.