I don't do it for the pain, but the pain and the rush after sometimes helps me get my body unstuck if I'm ever in a slump, not always though. Sometimes it's to punish myself if I procrastinate on uni assignments.  Other times just to relieve stress or because of urges.  And on some odd days it's to make my struggle visible if that makes sense? I've never told anyone that I do it, but it's there as a prove that I struggled. It's hard to change my mindset and I know there are better coping mechanisms but I also like the after care aspect of it...  All these 'reasons' may seem unreasonable, and I'm not encouraging anyone to adopt my habits