When I'm depressed, I think about death a lot. Not suicide. Just that we are all destined to die relatively soon.

That makes me wonder not only why we're here, but how can people get up and go to work or go shopping or anything, knowing, just knowing that we're going to die very soon?
Is it to distract themselves? Like if they stay busy or buy enough stuff, they don't have to think about it?

Very soon, we will cease to exist and the world will continue as though we were never born. How can anyone, sane or otherwise, not be depressed by that fact?