We've heard many people say and have often said ourselves that justice is doing one's own work and not meddling with what isn't one's own ... Then, i… - Plato

"Excellence" is not a gift, but a skill that takes practice.
We do not act "rightly" because we are "excellent",
in fact we achieve "excellence" by acting "rightly".

Parmenides: If anyone, with his mind fixed on all these objections and others like them, denies the existence of ideas of things, and does not assume an idea under which each individual thing is classed, he will be quite at a loss, since he denies that the idea of each thing is always the same, and in this way he will utterly destroy the power of carrying on discussion... Then what will become of philosophy? To what can you turn, if these things are unknown?

Then the case is the same in all the other arts for the orator and his rhetoric; there is no need to know the truth of the actual matters, but one merely needs to have discovered some device of persuasion which will make one appear to those who do not know to know better than those who know.