A quotation from Marcus Aurelius
The happiness of your life depends upon the quality of your thoughts: therefore, guard accordingly, and take care that you entertain no notions unsuitable to virtue and reasonable nature.
[Τὴν ὑποληπτικὴν δύναμιν σέβε. ἐν ταύτῃ τὸ πᾶν, ἵνα ὑπόληψις τῷ ἡγεμονικῷ σου μηκέτι ἐγγένηται ἀνακόλουθος τῇ φύσει καὶ τῇ τοῦ λογικοῦ ζῴου κατασκευῇ]
Marcus Aurelius (AD 121-180) Roman emperor (161-180), Stoic philosopher
Meditations [To Himself; Τὰ εἰς ἑαυτόν], Book 3, ch. 9 (3.9) (AD 161-180) [tr. Collier (1701)]
Sourcing, notes, alternate translations: wist.info/marcus-aureleus/2665…