A bald man was bit by a fly and hit his head trying to kill the fly. The fly mocked him for his injury but the man said he will endure more to kill the fly.
You will only injure yourself if you take notice of despicable enemies.
Eliot/Jacobs Version
There was once a Bald Man who sat down after work on a hot summer’s day. A Fly came up and kept buzzing about his bald pate, and stinging him from time to time. The Man aimed a blow at his little enemy, but acks palm came on his head instead; again the Fly tormented him, but this time the Man was wiser and said: “You will only injure yourself if you take notice of despicable enemies.”
Townsend version
A fly bit the bare head of a Bald Man who, endeavoring to destroy it, gave himself a heavy slap. Escaping, the Fly said mockingly, “You who have wished to revenge, even with death, the Prick of a tiny insect, see what you have done to yourself to add insult to injury?’ The Bald Man replied, “I can easily make peace with myself, because I know there was no intention to hurt. But you, an ill-favored and contemptible insect who delights in sucking human blood, I wish that I could have killed you even if I had incurred a heavier penalty.”
Heinrich Steinhöwel (Of the Bald-Headed Man and the Fly)
Perry: #525