An Ass bemoaned his treatment compared with a horse. The horse was taken into battle and died. The Ass thought better of his previous opinion.
Be content with your station.
Townsend version
An ass congratulated a Horse on being so ungrudgingly and carefully provided for, while he himself had scarcely enough to eat and not even that without hard work. But when war broke out, a heavily armed soldier mounted the Horse, and riding him to the charge, rushed into the very midst of the enemy. The Horse was wounded and fell dead on the battlefield. Then the Ass, seeing all these things, changed his mind, and commiserated the Horse.
Gherardo Image from 1480
Mulus et Equus
Mulus, conspiciens equum aureo freno ephippioque insignem et purpureis opertum phaleris, rumpebatur invidia, illum beatum reputans, qui continuo optimis vesceretur cibis et decoro amiciretur ornatu; se autem prae illo infelicem, qui, clitellis male dolatis oppressus, quotidie maxima onera ferre cogeretur. At ubi vidit equum pugna redeuntem, multis affectum vulneribus, prae illius calamitate se felicem appellabat, longe melius esse dicens quotidiano labore durum victum quaeritare et turpiter vestiri quam post optimos et delicatos cibos et tantos ornatus mortis adire discrimina.
Perry #357