A horse roamed freely in the meadows until one day, he was chased from his favored glen by a haughty stag. Angered, the horse went to a man and said "Man! There is a stag with whom I am at war. He is too powerful for either of us alone, but with my speed and your weapons, we could easily dispatch him." The man agreed, and after placing bridle and saddle on the horse, rode off and slew the stag. The horse said "What good fortune we found each other. Now if you would remove this bridle and saddle, we can go our separate ways." "Remove them? What sort of fool do you think I am? Hiyaa!"
Hence it is said: Vindicta pretiosa.
Notes
This is the second of the stories I remembered, without prompting, from Aesop, in my quest for short filler stories. To be honest, I don't actually remember this from Aesop, but from Asimov (it appears in "Bridle and Saddle", in Foundation). Because I remembered it from Asimov, I made the horse's enemy a wolf (which makes more sense, really); it wasn't until I checked Aesop that I discovered that it was a stag.