I doubt if a single individual could be found from the whole of mankind free from some form of insanity. The only difference is one of degree. A man who sees a gourd and takes it for his wife is called insane because this happens to very few people.
You want to hear about insanity? I was found running naked through the jungles in Mexico. At the Mexico City airport, I decided I was in the middle of a movie and walked out on the wing on takeoff. My body... my liver... okay, my brain... went.
Let us consider that we are all partially insane. It will explain us to each other; it will unriddle many riddles; it will make clear and simple many things which are involved in haunting and harassing difficulties and obscurities now.
How strange to have failed as a social creature -- even criminals do not fail that way -- they are the law's Loyal Opposition, so to speak. But the insane are always mere guests on earth, eternal strangers carrying around broken decalogues that they cannot read.
You must always be puzzled by mental illness. The thing I would dread most, if I became mentally ill, would be your adopting a common sense attitude; that you could take it for granted that I was deluded.