A bout of depression or a series of unfortunate events can certainly put you into a tail-spin that's difficult to get out of. I've been there; it's like you know what you need to do but something is weighing on you with such a force that it can be very difficult to fight against.

Ending up on the streets with nothing is a natural conclusion and what happens then is partly a test of character and partly luck. For many it's the end of the road.