Dionysius of Halicarnassus

From LSJ

ἀμήχανον δὲ παντὸς ἀνδρὸς ἐκμαθεῖν ψυχήν τε καὶ φρόνημα καὶ γνώμην, πρὶν ἂν ἀρχαῖς τε καὶ νόμοισιν ἐντριβὴς φανῇ → hard it is to learn the mind of any mortal or the heart, 'till he be tried in chief authority | it is impossible to know fully any man's character, will, or judgment, until he has been proved by the test of rule and law-giving

Source

Wikipedia EN

Dionysius of Halicarnassus (Ancient Greek: Διονύσιος Ἀλεξάνδρου Ἁλικαρνασσεύς, Dionúsios Alexándrou Halikarnasseús, Dionysios (son of Alexandros) of Halikarnassos; c.  60 BC – after 7 BC) was a Greek historian and teacher of rhetoric, who flourished during the reign of Emperor Augustus. His literary style was atticistic – imitating Classical Attic Greek in its prime.

Dionysius' opinion of the necessity of a promotion of paideia within education, from true knowledge of classical sources, endured for centuries in a form integral to the identity of the Greek elite.