I'm an overachiever, so everything is triggerable
Possible trigger:
My first time, which I don't remember, was when I was 5 and used a steak knife to cut my thigh screaming I hated how fat I was.
First time I remember SH was in 4th grade when I tried to intentionally sprain my wrist. I got caught by a teacher, but this was so long ago that no one knew it was a sign of distress. They just thought I was a whack job. (which of course I was

)
it became a habit in college, in addition to lots of other bad coping skills. Just today I was looking at my scars. They're very unobtrusive/easily "explained" (I have dozens of interesting but fake stories I can regail audiences with), but to me, they're a roadmap of how tragic my life has been, and the lengths to which I've gone to stay alive. I imagine, if I ever told my T that my favorite method is to cut away chunks of flesh with sharp scissors, she'd get a lot of insight.
Now quite old and in T for 4+ years, I don't act on my urges anymore. Sometimes I miss the outlet, so I fantasize about it. Sad. Very sad.