Depression is a very rational emotional state. Your life has no meaning, nothing you do matters, and you’re going to die. What’s not to be depressed about? 

Why not just kill yourself and be done with it? Seriously, I’m asking. Actually, as Camus suggests, you should be asking. “Why should I not kill myself?” That sounds like some pretty good self-inquiry right there, but maybe you shouldn’t jump right into the deep end of the pool. Start with something easier like, “Why should I not chew glass?” and work your way up.