Trivia: When Donnie is about to enter the car with Gretchen near the end of the film, he clutches at his stomach as if in pain, and we see Frank touch his eye after Donnie dies. Both these moments foreshadow pain: a deleted scene of Donnie's death shows a pole impaling his stomach right where he clutched it. And Donnie shoots Frank in the eye.
Donnie: Life isn't that simple. I mean who cares if Ling Ling returns the wallet and keeps the money? It has nothing to do with either fear or love.
Kitty Farmer: Fear and love are the deepest of human emotions.
Donnie: Okay. But you're not listening to me. There are other things that need to be taken into account here. Like the whole spectrum of human emotion. You can't just lump everything into these two categories and then just deny everything else!
Dr. Lilian Thurman: Donnie, an atheist is someone who denies altogether the existence of God. You're an agnostic. An agnostic is someone who believes that there can be no proof of the existence of God, but does not deny the possibility that God exists.