I guess what I mean is, sometimes the person doing it may not really be sure (in theory, I don't know for sure) and the ones overdosing on pills or whatever may full well expect that it will kill them. And, as weird as it may sound, people do survive gunshot wounds to the head, especially from smaller calibre / weaker rounds, like, say, a .22LR. I believe it's not unheard of for a .22LR round to literally bounce off the skull and cause fairly little serious damage.

And, of course it also complicates things that we can't talk to the people who succeed, and find out anything about their actual intentions. :-(