Enchiridion · §7

ὥσπερ ἐν πλῷ τοῦ πλοίου καθορμισθέντος εἰ ἐξέλθοις ὑδρεύσασθαι, ὁδοῦ δ᾽ ἐν παρέργῳ καὶ κοχλίδιον ἀναλέξαιο καὶ βολβάριον, δεῖ δέ σε τὸν νοῦν ἐπὶ τοῦ πλοίου ἔχειν καὶ συνεχῶς ἐπιστρέφεσθαι, μή ποτε ὁ κυβερνήτης καλέσῃ, κἂν καλέσῃ, πάντα ἐκεῖνα ἀφιέναι· οὕτω καὶ ἐν τῷ βίῳ, ἐὰν διδῶται ἀντὶ βολβαρίου γυναικάριον καὶ παιδίον, οὐδὲν κωλύει· ἐὰν δὲ ὁ κυβερνήτης καλέσῃ, τρέχε ἐπὶ τὸ πλοῖον ἀφεὶς ἐκεῖνα ἅπαντα μηδὲ ἐπιστρεφόμενος.

hōsper en plō tou ploiou kathormisthentos ei exelthois hudreusasthai, hodou d' en parergō kai kochlidion analexaio kai bolbarion, dei de se ton noun epi tou ploiou echein kai sunechōs epistrephesthai, mē pote ho kubernētēs kalesē, kan kalesē, panta ekeina aphienai; houtō kai en tō biō.

Consider how it is when a ship is in harbor: if you go ashore to collect water and happen to pick up a shellfish or a small bulb along the way, you must keep your attention on the ship and keep watching for the captain's call. If he calls, you must let go of all those things and run back, without even turning to look. So too in life: if instead of a shellfish you are given a wife and child, nothing prevents that — but if the captain calls, you must run to the ship, leaving everything behind, without a backward glance.

— Enchiridion 7

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