An act, by which we make one friend and one enemy, is a losing game; because revenge is a much stronger principle than gratitude.

Gains and losses in goodwill are not symmetrical. The person you helped will feel warmly about it for a while and then absorb it into the ordinary background, while the person you crossed will remember with much greater precision and for much longer. A decision that pleases one person and injures another usually leaves you worse off, even when it looked even at the time. The books do not balance the way the arithmetic suggests.

Before an action that will divide people, weigh the enemy more heavily than the friend. If you can get the same result without making anyone an opponent, that version is worth some inconvenience.