Aporrembesthai

Μὴ κατατρίψῃς τὸ ὑπολειπόμενον τοῦ βίου μέρος ἐν ταῖς περὶ ἑτέρων φαντασίαις, ὁπόταν μὴ τὴν ἀναφορὰν ἐπί τι κοινωφελὲς ποιῇ. ἤτοι γὰρ ἄλλου ἔργου στέρῃ, τουτέστι φανταζόμενος τί ὁ δεῖνα πράσσει καὶ τίνος ἕνεκεν καὶ τί λέγει καὶ τί ἐνθυμεῖται καὶ τί τεχνάζεται καὶ ὅσα τοιαῦτα ποιεῖ ἀπορρέμβεσθαι τῆς τοῦ ἰδίου ἡγεμονικοῦ παρατηρήσεως.
(Marcus Aurelius, Ta eis heauton 3.4.1)

Don’t waste the rest of your time here worrying about other people – unless it affects the common good. It will keep you from doing anything useful. You’ll be too preoccupied with what so-and-so is doing, and why, and what they’re saying, and what they’re thinking, and what they’re up to, and all the other things that throw you off and keep you from focusing on your own mind. (tr. Gregory Hays)