Enchiridion · §38

ὡς ἐν τῷ βαδίζειν ἐπιμελῇ μὴ ἐπιβῆναι ἥλῳ ἢ στρέψαι τὸν πόδα, οὕτως ἐπιμελοῦ μὴ βλάψαι τὸ ἡγεμονικόν σου. καὶ ἐὰν τοῦτο παραφυλάσσωμεν ἐφ᾽ ἑκάστου ἔργου, ἀσφαλέστερον ἁψόμεθα τοῦ ἔργου.

hōs en tō badizein epimelē mē epibēnai hēlō ē strepsai ton poda, houtō epimelou mē blapsai to hēgemonikon sou. kai ean touto paraphulassōmen eph' hekastou ergou, asphalesteron hapsometha tou ergou.

Just as you are careful when walking not to step on a nail or twist your ankle, be equally careful not to damage your ruling faculty. And if we keep this vigilance in every action, we will undertake our work more safely.

— Enchiridion 38

Source: Greek (Schenkl/Oldfather critical edition tradition) + Long 1877 English translation