The major problem with depression is not lack of belief than one should overcome it, but lack of belief that one can overcome it.

Another problem is that sometimes it isn't seen as depression. There's a version (sometimes I call it an attack of the bleaks) where it seems as though it's acceptance of hard truths. The problem is that a highly negative take on the situation is so emotionally attractive that it blanks out optimistic outcomes.Or maybe there's something biochemical going on which makes positive futures not be emotionally salient.