“No one, not even a ‘friend,’ can make us better. But it is a great happiness in life to meet a person of quite different construction, different bent, completely dissimilar views who, while always remaining himself and in no wise echoing us nor currying favor with us (as sometimes happens) and not trying to insinuate his soul (and an insincere soul at that!) into our psyche, into our muddle, into our tangle, would stand as a firm wall, as a check to our follies and our irrationalities, which every human being has. Friendship lies in contradiction and not in agreement!”

Note to a letter of Strakhov dated January 5, 1890, in his book Literary Exiles. Via brainpickings.