It's amazing to me how many of the comments on this thread remind me of how I would describe depression.
I'm not poor and never have been. But I have felt hopeless despair that I don't think people can understand unless they've experienced it. It is an emotional response that is radically disproportionate to the actual circumstances that triggered it.
I won't argue that depression has any of the long-term effects you describe though.
I agree though, it's like describing what color is to a person blind from birth. In some cases (as are represented on this thread) it's like describing it to a blind person who thinks they already know how all the senses work, and a person can just get over the "seeing thing" if they just sniff hard enough.