Letter 828: Virtue must be practiced with all one's strength — not merely admired from a distance.

To Apollonios. I say that flattery is more powerful and more grievous than fear. For what compulsion cannot accomplish, fawning service can; and those who have not been subdued by fear, flattery has often enslaved. One must therefore play the man against both fear and fawning service (for each of these passions is the mark of a slave), and honor truth alone.

Ἐγὼ τοῦ φόβου τὴν κολακείαν δυνατωτέραν καὶ ἀργαλεωτέραν εἶναί φημι. Ὅσα γὰρ μὴ δύναται ἀνάγκη, δύναται θεραπεία· καὶ τοὺς μὴ χειρωθέντας ὑπὸ φόβου, κολακεία πολλάκις κατεδουλώσατο. Χρὴ οὖν καὶ πρὸς φόβον καὶ πρὸς θεραπείαν μὲν ἀνδρίζεσθαι (ἑκάτερον δὲ ἀνελεύθερον τὸ πάθος), τὴν δ' ἀλήθειαν μόνην τιμᾷν.