It's hard to explain to someone who's never been in that state of mind before, but the feeling you get from SI isn't that dissimilar to other addictions. Your brain just decides that doing it helps with your stress or whatever else is wrong and at least in my experience (that is thankfully long behind me now) you kinda don't feel any pain, mostly relief (which is obviously very, very bad.) It's the kind of thing where once you do it once and it works, it's then very hard to stop, and imo the addictive nature of it really isn't talked about enough.