Susan and Death's entire conversation about humanity and belief:
Susan: All right. I'm not stupid. You're saying humans need... fantasies to make life bearable.
Death: Really? As if it was some kind of pink pill? No. Humans need fantasy to be human. To be the place where the falling angel meets the rising ape.
Susan: Tooth fairies? Hogfathers? Little-
Death: Yes. As practice. You have to start out learning to believe the little lies.
Susan: So we can believe the big ones?
Death: Yes. Justice. Mercy. Duty. That sort of thing.
Susan: They're not the same at all!
Death: You think so? Then take the universe and grind it down to the finest powder and sieve it through the finest sieve and then show me one atom of justice, one molecule of mercy. And yet- And yet you act as if there is some ideal order in the world, as if there is some rightness in the universe by which it may be judged.
Susan: Yes, but people have got to believe that, or what's the point-
Death: My point exactly. There is a place where two galaxies have been colliding for a million years. Don't try to tell me that's right.
Susan: Yes, but people don't think about that. Somewhere there was a bed...
Death: Correct. Stars explode, worlds collide, there's hardly anywhere in the universe where humans can live without being frozen or fried, and yet you believe that a bed is a... a normal thing. It is the most amazing talent.
Death: Oh, yes. A very special kind of stupidity. You think the whole universe is inside your heads.
Susan: You make us sound mad.
Death: No. You need to believe in things that aren't true. How else can they become?