sometimes success is the worse thing that can happen to a depressed person. normal depressed people always say 'i'd be happy if,,,,,' and then they talk about being rich, famous, whatever. it gives them a dream.
when you succeed in everything you do, and you are still depressed you are fukked. you realize nothing will get rid of it. there is no unlikely occurance that you can imagine to pull you out of this state. anything that would make it better - you've already achieved.
litterally, they think,' well this is as good as it gets, and it's not good enough'.