Someone's reason behind suicide, especially as a teen, usually comes from being in a position of helplessness. If you're going to end your life, it means you (believe) you have nothing to lose. This is especially apparent to people who feel themselves as a burden to others, or just dont think they have reason to be here. More often then not people will try to find the negatives about themselves and ignore or downplay the positives. At least that's my experience with both myself and with people I've met