Enchiridion · §6

ἐπὶ μηδενὶ ἀλλοτρίῳ ἀγαθῷ ἐπαίρου. εἰ ὁ ἵππος ἐπαιρόμενος ἔλεγεν ὅτι "καλός εἰμι", οἰστὸν ἄν. σὺ δὲ ὅταν λέγῃς ἐπαιρόμενος ὅτι "καλὸν ἵππον ἔχω", ἴσθι ὅτι ἐπὶ ἵππου ἀγαθῷ ἐπαίρῃ. τί οὖν ἐστι σόν; χρῆσις φαντασιῶν. ὥσθ᾽ ὅταν ἐν χρήσει φαντασιῶν κατὰ φύσιν σχῇς, τότε ἐπάρῃ· τότε γὰρ ἐπὶ σῷ τινι ἀγαθῷ ἐπαρθήσῃ.

epi mēdeni allotriō agathō epairou. ei ho hippos epairomenos elegen hoti 'kalos eimi', oiston an. su de hotan legēs epairomenos hoti 'kalon hippon echō', isthi hoti epi hippou agathō epairē. ti oun esti son? chrēsis phantasiōn.

Never take pride in a distinction that belongs to someone else. If a horse could speak and said 'I am beautiful,' that would be tolerable — the beauty is its own. But when you say proudly 'I have a fine horse,' know that you are taking pride in the horse's quality, not your own. So what actually belongs to you? The use you make of your impressions. Whenever you are in accord with nature in how you use your impressions, then and only then take pride — for then you will be proud of something genuinely yours.

— Enchiridion 6

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