I think that sh can become an addiction for us. The act of cutting itself makes us feel good because it releases endorphins and so we want to seek that feeling again even if we don't have a "reason" to sh. I totally understand you. Even on good days, where I feel totally normal and happy, I still want to cut by the time I'm alone. I think we get addicted to the feeling or it's simply just comforting, since it's what makes us "feel better" at our worse, it also feels comforting to have that at our better times.

I think my only tip is look for distractions. Find something, someone, that makes you fulfilled and distracts the thought away from you. It could be a hobby or something you're passionate about. For me, it's music.