There is one vice of which no man in the world is free; which everyone in the world loathes when he sees it in someone else; and of which hardly any people, except Christians, ever imagine that they are guilty themselves.
I have heard people admit that they are bad-tempered, or that they cannot keep their heads about girls or drink, or even that they are cowards. I do not think I have ever heard anyone who was not a Christian accuse himself of this vice. And at the same time I have very seldom met anyone, who was not a Christian, who showed the slightest mercy to it in others. There is no fault which makes a man more unpopular, and no fault which we are more unconscious of in ourselves. And the more we have it in ourselves, the more we dislike it in others. … The vice I am talking of is Pride or Self-Conceit. … Pride leads to every other vice: it is the complete anti-God state of mind.
-C. S. Lewis, Mere Christianity