Plato, Meno 98c

οὐδὲν ἄρα ὀρθὴ δόξα ἐπιστήμης χεῖρον οὐδὲ ἧττον ὠφελίμη ἔσται εἰς τὰς πράξεις, οὐδὲ ἁνὴρ ὁ ἔχων ὀρθὴν δόξαν ἢ ὁ ἐπιστήμην. ἔστι ταῦτα. καὶ μὴν ὅ γε ἀγαθὸς ἀνὴρ ὠφέλιμος ἡμῖν ὡμολόγηται εἶναι. ναί. ἐπειδὴ τοίνυν οὐ μόνον διʼ ἐπιστήμην ἀγαθοὶ ἄνδρες ἂν εἶεν καὶ ὠφέλιμοι ταῖς πόλεσιν, εἴπερ εἶεν, ἀλλὰ καὶ διʼ ὀρθὴν δόξαν, τούτοιν δὲ οὐδέτερον φύσει ἐστὶν τοῖς ἀνθρώποις,

So that right opinion will be no whit inferior to knowledge in worth or usefulness as regards our actions, nor will the man who has right opinion be inferior to him who has knowledge. That is so. And you know that the good man has been admitted by us to be useful. Yes. Since then it is not only because of knowledge that men will be good and useful to their country, where such men are to be found, but also on account of right opinion; and since neither of these two things—knowledge