“Whatever one of us asked the other to do - it was assumed the asker would weigh all the consequences - the other would do. Thus one might wake the other in the night and ask for a cup of water; and the other would peacefully (and sleepily) fetch it. We, in fact, defined courtesy as 'a cup of water in the night'. And we considered it a very great courtesy to ask for the cup as well as to fetch it.”