Depression?

So
I read somewhere that when people are going through a breakdown or dealing with stress or depression, when they feel down they 'reward' themselves. Whether it's eating, getting to sleep all day, not having to do their usual work, etc etc.

I also think that people 'punish' themselves just the same. Cutting, burning, emotionally terrorizing themselves..

My question is, where do the other reactions fit in? Smoking, alcohol, drugs?

They're rewarding themselves, because it's something that they enjoy doing and sometimes know it's not right but do it anyway..

but then again, they're also slowly killing themselves. I also read somewhere that whenever people smoke it's because they have a psychological, sometimes very hidden, want to kill themselves.

People know what affects these things have on them, yet they do it anyway. Is it simply addiction? Rewarding themselves? Punishing themselves? All of the above? What do you guys think?

xxox Courtney