The First [Friend] is the alter ego, the man who first reveals to you that you are not alone in the world by turning out (beyond hope) to share all your most secret delights. There is nothing to be overcome in making him your friend; he and you join like raindrops on a window. But the Second Friend is the man who disagrees with you about everything... Of course he shares your interests; otherwise he would not become your friend at all. But he has approached them all at a different angle. he has read all the right books but has got the wrong thing out of every one... How can he be so nearly right, and yet, invariably, just not right? He is as fascinating (and infuriating) as a woman.

Surprised by Joy (1955)