Mastodawn

Don’t let the future disturb you. You will meet it, if you have to, with the same weapons of reason which today arm you against the present.

[Τὰ μέλλοντα μὴ ταρασσέτω· ἥξεις γὰρ ἐπ᾿ αὐτά, ἐὰν δεήσῃ, φέρων τὸν αὐτὸν λόγον, ᾧ νῦν πρὸς τὰ παρόντα χρᾷ.]

Marcus Aurelius (AD 121-180) Roman emperor (161-180), Stoic philosopher
Meditations [To Himself; Τὰ εἰς ἑαυτόν], Book 7, ch. 8 (7.8) (AD 161-180) [tr. Coker (2022)]