Sad people
There are many sad people in this world, and they can't be helped. They can't be helped because they don't want to be helped. At this point their being sad is a part of their image. It's integrated and cannot be easily removed.
You might have tried to help people like this in the past. You've listened, you've given some simple advice. You've nodded while they described how their situation is just so bad. That it's all this way because of some event from the past, their hard upbringing, or some person who did something terrible to them. Besides, the system is rigged, everybody knows that.
You might have seen them heading for a train wreck of some kind. Maybe the person torpedoed their own chances to achieve something. Maybe they dumped some of their last cash to some worthy cause. It was strange, but you've chalked it up to bad luck or moment of weakness. I mean, nobody would just give up in order to hurt themselves, right?
The truth that I've come to understand is that, in fact, there are many people doing, unconsciously or not, exactly that. No amount of good energy or cheering up will do anything. It's often not about the nail.
If you try to push back a little, they might take it as an offense. They might tell you things like "what can you know, you had it easy from the start", or "you just don't know about how it's like, you have x/y/z to help you". Anger is a strong emotion, don't ask how I know.
I'm not saying those people are bad or evil. I'm not pointing fingers, I'm the first to acknowledge that self-pity is, contrary to appearances, a quite pleasant thing to do. It takes energy and focus to repair something, or at least be placid in trying times. It takes a lot of work to train that in oneself, and it's a lifetime work.
It's not as easy as letting go of this person. It might be your parent. It might be your sibling. It might be you (me). But what is important I think is to realize that it's happening.
There might be times when we need to cry a little, to be heard, to be understood, to be helped. There are times when everything is grey-ish no matter what's the weather. It's normal.
But sometimes we just try to fill up an unfillable void.