Meditations, Book 11, Section 16

Marcus Aurelius — The Emperor

The closer something is to being free from passion, the more powerful it becomes. Both grief and anger come from weakness. When you get angry or grieve, you have taken a wound. You have given in to your feelings like a coward. Here is a tenth lesson from Hercules, leader of the Muses: it is madness to expect there to be no wicked people in the world. That is impossible. But to accept that wicked people exist while refusing to tolerate any wrong against yourself — that is unfair and tyrannical.

Marcus Aurelius — The Emperor Original

For the nearer everything is unto unpassionateness, the nearer it is unto power. And as grief doth proceed from weakness, so doth anger. For both, both he that is angry and that grieveth, have received a wound, and cowardly have as it were yielded themselves unto their affections. If thou wilt have a tenth also, receive this tenth gift from Hercules the guide and leader of the Muses: that is a mad man's part, to look that there should be no wicked men in the world, because it is impossible. Now for a man to brook well enough, that there should be wicked men in the world, but not to endure that any should transgress against himself, is against all equity, and indeed tyrannical.