Once you have your first suicidal thought, you've did it, you've won at life. Nothing scares you anymore. Death is just another friend, maybe the only one. You start going through life fearlessly, and thus confidently. You're no longer afraid to take chances, because what's the worst case? You die? You've already been there. It's not that scary. The death of others no longer saddens you. Some may say this is a downside, but I think it's an advantage.
Also, suicidal thoughts usually occur when you hit the bottom, or when you think you did. You think that it can't get worse than this, and if you survived, everything that comes later is by definition better than what you were going through.