I struggled a tremendous amount with depression and suicidal thoughts, and was a self-harmer for many years. I don't really know what kept me from actually ACTING on it... I can't say "oh, my family kept me from doing it," because honestly, that wasn't my frame of mind... and it's not the frame of mind of those who actually go through with it. I guess whatever just "clicks" in the minds of those who do it just never did for me. Those people, they lose rational thought. It makes everyone feel worse to say, "oh, look at those they left behind", but that's not how it goes... they're so sick at that point, that all rational thought is gone.
My best friend in college was an officer in the Marines. He called me from Iraq every chance he got. I could tell he was having a tough time coping, but he wouldn't really talk. One day, he called me, told me he loved me and that I shouldn't worry about him. Then he hung up the phone, and he shot himself. I will never forget how detached he sounded at the end. I felt so much regret for a long, long time... but in talking to others with PTSD and survivors, I've come to terms with the fact that there was NOTHING I could have said. Not because he'd made a decision, per se, but because rational thought wasn't even there.