At first, I'd try to explain that it's not really negativity or sadness anymore, it's more just this detached, meaningless fog where you can't feel anything about anything — even the things you love, even fun things — and you're horribly bored and lonely, but since you've lost your ability to connect with any of the things that would normally make you feel less bored and lonely, you're stuck in the boring, lonely, meaningless void without anything to distract you from how boring, lonely, and meaningless it is.This is a nearly perfect explanation of what it is like to be depressed. The sense of nothingness & deadening of feeling is captured perfectly. Go read it if you know someone who is depressed or you've experienced the crushing weight of depression yourself.
And that's the most frustrating thing about depression. It isn't always something you can fight back against with hope. It isn't even something — it's nothing. And you can't combat nothing. You can't fill it up. You can't cover it. It's just there, pulling the meaning out of everything. That being the case, all the hopeful, proactive solutions start to sound completely insane in contrast to the scope of the problem.