“My argument against God was that the universe seemed so cruel and unjust. But how had I got this idea of just and unjust? A man does not call a line crooked unless he has some idea of a straight line. What was I comparing this universe with when I called it unjust? If the whole show was bad and senseless from A to Z, so to speak, why did I, who was supposed to be part of the show, find myself in such a violent reaction against it? A man feels wet when he falls into water because man is not a water animal: a fish would not feel wet. Of course, I could have given up my idea of justice by saying it was nothing but a private idea of my own. But if I did that, then my argument against God collapsed too— for the argument depended on saying that the world really was unjust, not simply that it did not happen to please my private fancies. Thus in the very act of trying to prove that God did not exist— in other words, that the whole of reality was senseless— I found I was forced to assume one part of reality— namely my idea of justice— was full of sense.”
C.S. Lewis, The Joyful Christian
via Douglas Wilson and Randy Booth. A Justice Primer (Second Edition).