Enchiridion · §19

ἀνίκητος εἶ ἐὰν εἰς μηδένα ἀγῶνα κατέλθῃς, ὃν οὐκ ἔστιν σου ἐπὶ σοί γενέσθαι νικῆσαι. ὅρα μὴ θεασάμενός τινα τιμώμενον ἢ μεγάλα δυνάμενον ἢ ἄλλως εὐδοκιμοῦντα ἐπαρθῇς ὑπὸ τῆς φαντασίας καὶ μακάριον αὐτὸν ὑπολαμβάνῃς. ἂν γὰρ ἐν τοῖς ἐφ᾽ ἡμῖν ᾖ τὸ ἀγαθόν, οὐδὲ ζηλοτυπίᾳ οὐδὲ φθόνῳ τόπος ἔσται· σὺ δ᾽ αὐτὸς οὐ στρατηγὸς θελήσεις οὐδὲ πρύτανις οὐδὲ ὕπατος, ἀλλὰ ἐλεύθερος.

anikētos ei ean eis mēdena agōna katelthēs, hon ouk estin sou epi soi genesthai nikēsai. hora mē theasamenos tina timōmenon ē megala dunamenon ē allōs eudokimounta eparthēs hupo tēs phantasias. an gar en tois eph' hēmin ē to agathon, oude zēlotupia oude phthonō topos estai; su d' autos ou stratēgos thelēseis, alla eleutheros.

You are invincible if you enter no contest you cannot win. When you see someone honored, powerful, or held in high esteem, take care that you are not carried away by the impression and count him happy. For if the good lies in what is truly ours, there is no room for envy or jealousy — and you yourself will not wish to be a general, a senator, or a consul, but to be free.

— Enchiridion 19

Source: Greek (Schenkl/Oldfather critical edition tradition) + Long 1877 English translation