Epictetus · The Handbook
Chapter 6
Do not be proud of any excellence that is not your own. If a horse said proudly, “I am beautiful,” it would be bearable. But when you say proudly, “I have a beautiful horse,” understand: you are proud of a good that belongs to a horse. What, then, is yours? The use of impressions. So when you handle your impressions in harmony with nature, then be proud – for then you will be proud of a good that is your own.
ἐπὶ μηδενὶ ἐπαρθῇς ἀλλοτρίῳ προτερήματι. εἰ ὁ ἵππος ἐπαιρόμενος ἔλεγεν ὅτι «καλός εἰμι,» οἰστὸν ἂν ἦν· σὺ δέ, ὅταν λέγῃς ἐπαιρόμενος ὅτι «ἵππον καλὸν ἔχω,» ἴσθι, ὅτι ἐπὶ ἵππου ἀγαθῷ ἐπαίρῃ. τί οὖν ἐστι σόν; χρῆσις φαντασιῶν. ὥσθ’, ὅταν ἐν χρήσει φαντασιῶν κατὰ φύσιν σχῇς, τηνικαῦτα ἐπάρθητι· τότε γὰρ ἐπὶ σῷ τινι ἀγαθῷ ἐπαρθήσῃ.