"Would you say a man deserves to be a physician at the moment when he makes a mistake in treating his patient and just in respect of that mistake; or a mathematician, when he does a sum wrong and just in respect of that mistake. . . ." Republic, I, 340. Cornford tr.
If he wasn't a physician when he was making a mistake it wouldn't be a mistake.
I find Plato wonderful -- but that hardly requires agreeing with him.
Carrol