The Horse and the Stag

At one time the horse had the plain entirely to himself. Then a stag
intruded into his domain and shared his pasture. The horse, desiring to
revenge himself on the stranger, asked a man if he were willing to
help him in punishing the stag. The man replied that if the horse would
receive a bit in his mouth and agree to carry him, he would contrive
effective weapons against the stag. The horse consented and allowed
the man to mount him. From that hour he found that instead of obtaining
revenge, he'd enslaved himself to the service of man.