Also from Orthodoxy.:
"THE Christian admits that the universe is manifold and even miscellaneous, just as a sane man knows that he is complex. Nay, the really sane man knows that he has a touch of the madman. But the Materialist's world is quite simple and solid, just as the madman is quite sure he is sane. The Materialist is sure that history has been simply and solely a chain of causation, just as the interesting person before mentioned is quite sure that he is simply and solely a chicken. Materialists and madmen never have doubts."
Every one who has had the misfortune to talk with people in the heart or on the edge of mental disorder, knows that their most sinister quality is a horrible clarity of detail; a connecting of one thing with another in a map more elaborate than a maze. If you argue with a madman, it is extremely probable that you will get the worst of it; for in many ways his mind moves all the quicker for not being delayed by the things that go with good judgment. He is not hampered by a sense of humour or by charity, or by the dumb certainties of experience. He is the more logical for losing certain sane affections. Indeed, the common phrase for insanity is in this respect a misleading one. The madman is not the man who has lost his reason. The madman is the man who has lost everything except his reason.-- Orthodoxy.