Whats wrong with suicide?

i have nothing against suicide as long as its done by adults. Sure, some people wouldn't like it but what if it puts the person out of his misery? Isn't that better than getting him to live a life of sadness? Some people say its selfish, and it would only hurt himself and other people, especially family and friends, but i think in the long run it would be the individual who would be hurting the most. When nobody understands how he feels, or he's tired of pretending to be ok all the time it would be a slow painful torture. Thats why he would choose to kill himself for. i think it would be best to be sad for a short amount of time than to live a long life of sadness and hurt.