Whenever someone has done wrong by you, immediately consider what notion of good or evil they had in doing it. For when you see that, you’ll feel compassion, instead of astonishment or rage. For you may yourself have the same notions of good and evil, or similar ones, in which case you’ll make an allowance for what they’ve done. But if you no longer hold the same notions, you’ll be more readily gracious for their error.

Marcus Aurelius

Hat tip to lifehacker.