Plutarch, Life of Numa
5.2 (tr. Bernadotte Perrin):
Every change in a man's life is perilous; but when a man knows no lack, and has no fault to find with his present lot, nothing short of madness can change his purposes and remove him from his wonted course of life, which, even though it have no other advantage, is at least fixed and secure, and therefore better than one which is all uncertain.
πᾶσα μὲν ἀνθρωπίνου βίου μεταβολὴ σφαλερὸν ᾧ δὲ μήτ᾽ ἄπεστί τι τῶν ἱκανῶν μήτε μεμπτόν ἐστι τῶν παρόντων, τοῦτον οὐδὲν ἄλλο πλὴν ἄνοια μετακοσμεῖ καὶ μεθίστησιν ἐκ τῶν συνήθων οἷς κἂν εἰ μηδὲν ἕτερον προσείη.