First, that human beings, all over the earth, have this curious idea that they ought to behave in a certain way, and cannot really get rid of it. Secondly, that they do not in fact behave in that way. They know the Law of Nature; they break it. These two facts are the foundation of all clear thinking about ourselves and the universe we live in.
Lewis, C. S.. Mere Christianity (C.S. Lewis Signature Classics) (p. 8). HarperCollins. Kindle Edition.