Epictetus' Discourses Vol. 2 (Books 3-4) & Encheiridion

...or, if it should so happen, a nightingale. In general, one might not improperly declare that each thing is beautiful at that time when it is in its best state according to its own nature. But since the nature of each thing is different, it seems to me that each of them is beautiful in a different way.
4 Is that not so? — He agreed. — Therefore, what makes a dog beautiful makes a horse ugly, and what makes a horse beautiful makes a dog ugly, since their natures are different?
5 — It seems so. — For I think that what makes a pancratiastoriginal: pagkratiastēn; an athlete specializing in a sport combining boxing and wrestling beautiful makes a wrestler a poor one, and would make a runner look most ridiculous. And the same man who is beautiful for the pentathlonoriginal: pentathlian; a five-event contest consisting of leaping, running, wrestling, discus, and javelin is most ugly for wrestling?
6 — That is so, he said. — What then makes a human being beautiful? Is it not the same thing that makes a dog or a horse beautiful in its own kind? — It is, he said. — What then makes a dog beautiful? The presence of a dog’s excellenceoriginal: aretē; often translated as "virtue," it refers to the functional perfection or "goodness" of a thing. What makes a horse beautiful? The presence of a horse’s excellence. What then makes a human being beautiful? Is it not the presence of a human’s excellence?
7 And so, young man, if you wish to be beautiful, you must work on this: human excellence.
8 — And what is this? — See whom you yourself praise when you praise people without being biased by passion. Do you praise the just or the unjust? — The just. — The temperateoriginal: sōphronas; those who possess self-control and moderation or the dissipated? — The temperate. — The self-controlledoriginal: enkrateis; those with mastery over their desires
9 or the undisciplined? — The self-controlled. — Know then, that by making yourself such a person, you make yourself beautiful;

¹ One who specialized in the pancratium, a combination of boxing, wrestling, and plain "fighting."