Self-consciousness is the culprit. It is clear to our inner critic that we really should be doing these "constructive to-dos". Guilt is the result when the list (whatever its contents are) is left unchecked. The longer you wait, the more shame of one self builds up. You feel increasingly worthless, and soon at a total loss in face of the daunting task. Depression is a very likely outcome from this scenario. Of course it's not the only way we hit rock bottom, but it is however factually true that people who score high in self awareness, also experience negative emotions more often.
First thing those who suffer from depression should consider doing is taking some kind of antidepressant. Their chemical cocktail is off balance and could need a helping hand. It's not cheating, it's effective. Because if someone is really, REALLY depressed, then he can barely imagine a frame of mind in which he is not flawed. Medicine makes you more receptible to advice.
Ultimately though, when it comes down to it, the ill individual must get going doing productive, worthwhile things. If he feels he's beyond saving, then he must do SOMETHING. Anything to get him out of his own head. Human company is great. But what you want ideally, is an upward going spiral which only begins by managing small tasks in order to increase motivation and self-worth.
The exact recipe is heavily dependent on the individual, though. Is it you own opinion that matter more, or the affirmations of people around you? Do you simply feel unable, or is it your genes which are not up to par? There is no surefire way.
Now, instead of trying to live up to one's own ego, one could just get rid of it xD. Not that it's at all obvious how one would go about doing just that. I would start by asking "Why do you really hate yourself so? What about this whole affair called living is so serious that you must look down at just the mention of your name? Why run away from your self by binge-watching or getting drunk? What's so bad about you? Well, aren't your friends just as bad? Do they not do just the same? Don't they criticize themselves?"