Epictetus · Discourses 52.2
Have you a wild beast's disposition, the urge for revenge? A horse is not wretched when he cannot crow but when he cannot run. A dog, not when he cannot fly but when he cannot track.
What this means
An animal is wretched not when it lacks some other creature's gift but when it cannot do its own proper work, a horse that cannot run, a dog that cannot track. Epictetus turns the mirror on us: a person's proper work is reason, so the urge for revenge is the human version of a horse forgetting how to run. Anger is not strength here; it is malfunction.
On nature, judgment, anger.