Plato, Meno 71a

ἐκ τῶνδε τῶν τόπων παρʼ ὑμᾶς οἴχεσθαι ἡ σοφία. εἰ γοῦν τινα ἐθέλεις οὕτως ἐρέσθαι τῶν ἐνθάδε, οὐδεὶς ὅστις οὐ γελάσεται καὶ ἐρεῖ· ὦ ξένε, κινδυνεύω σοι δοκεῖν μακάριός τις εἶναι—ἀρετὴν γοῦν εἴτε διδακτὸν εἴθʼ ὅτῳ τρόπῳ παραγίγνεται εἰδέναι—ἐγὼ δὲ τοσοῦτον δέω εἴτε διδακτὸν εἴτε μὴ διδακτὸν εἰδέναι, ὥστʼ οὐδὲ αὐτὸ ὅτι ποτʼ ἐστὶ τὸ παράπαν ἀρετὴ τυγχάνω εἰδώς.

a drought of wisdom, as it were, has come on; and it seems as though wisdom had deserted our borders in favour of yours. You have only to ask one of our people a question such as that, and he will be sure to laugh and say: Stranger, you must think me a specially favoured mortal, to be able to tell whether virtue can be taught, or in what way it comes to one: so far am I from knowing whether it can be taught or not, that I actually do not even know what the thing itself, virtue, is at all.