For me, I'd SIed a couple of times in a few days, discussed it with my therapist, and said "well as I have no good reason for injuring myself, and as I prefer not to do things without a good reason, I'll stop" and then it was 'easy' as I'd promised I'd stop, I just had to keep that promise. I try to never break a promise.
Of course when I did SI myself a few months later I felt really bad about it because I'd broken the promise.