Letter 477: When someone treats you unjustly, Athanasios, the natural response is to respond in kind.

To Athanasios. On flattery. I learn that flatterers hang upon your tongue, swearing on the one hand that it would be best of all, even if you chose to admire one of the most absurd of evils, but on the other hand reviling you as quickly as may be, even should you disparage virtue itself. If, then, you are not willing to be persuaded by us, yet at least be persuaded by Isocrates [the Athenian orator, 436-338 BC], who exhorted men to hate those who flatter, just as they hate those who deceive. For both alike, once they have been trusted, wrong those who trusted them.

Περὶ κολακείας. Πυνθάνομαι ὅτι κόλακες ἐξήρτηνται τῆς σῆς γλώττης, ὀμνύντες μέν, ὅτι πάντων ἄριστον εἴη, εἰ καὶ τι τῶν ἀτοπωτάτων ἔλοιο θαυμάσαι κακῶν· καχίζοντες δὲ (23) ᾗ τάχος, εἰ καὶ αὐτὴν ἐκκακύνοις τὴν ἀρετήν. Εἰ τοίνυν μὴ ἐθέλεις ἡμῖν πεισθῆναι, ἀλλά γε κἂν Ἰσοκράτει πείσθητι, παραινέσαντι μισεῖν τοὺς κολακεύοντας, ὥσπερ τοὺς ἐξαπατῶντας. Ἀμφότεροι γὰρ πιστευθέντες, τοὺς πιστεύσαντας ἀδικοῦσι.