It perplexes me how shit goes in their mind, when they seem to have so much to live for. I know that suicide is rarely a so-called "rash" decision. The truth is that a lot of people have already decided to end it long before they actually do, but then hang around awhile longer so that they can tend to relationships, give friends and family some positive 'most-recent' memories to leave them with, which usually ends-up just confusing them even more (i.e. I can't believe he did this, the past few weeks he seemed to be so upbeat, he even came over just to say hello or help me do this or that). This is sometimes their way of saying goodbye and hope you don't hate them too much for it.
Suicide just....stinks. There are sometimes reasons which I can understand. A classmate of mine killed himself a few years ago but he had received dx of terminal cancer and was starting to feel some of the changes in his body due to it. He didn't tell anyone except a couple people (about his diagnosis, not his intent to suicide).