I think there are some people who are inherently sad. People are born with their fair share of woes but there are some among them who seek out the darkness. There are some who choose to be happy no matter what and there are some that struggle to find happiness but still try. And then there are those who are addicted to the darkness. They feed off their unhappiness and misery. Even when they have something good they seek to destroy it because they probably believe they need to be punished for being happy. They are lost without their pain.
How do you help someone like this?