Letter 840: Vice needs no teacher — it comes naturally to our fallen nature.

To Zosimos. Since you behave much like an incurable disease that, once it has gained the upper hand, spares nothing that it craves, but bids the physicians farewell and thrusts itself forward out of the very ruin it has stirred up for itself, for this reason your return to self-control [sophrosyne] seems difficult for you. But if you would cease from the luxury that drives you mad with the goad of passion (for this is the root of licentiousness, and stands as its mother), then the flame of debauchery too will be quenched. For once the whole supply has been removed, the fire that grows and rises to its peak from it will plainly be extinguished as well. But if you yourself keep furnishing the whole supply to the fire, how will it abate and cease? If you yourself rouse the beast when it is at rest, who is to tame it once it is stirred up and raging? Therefore, considering these things and what is akin to them, cease from your perpetual indulgence in luxury.

Ἐπειδὴ παραπλησίον τι ποιεῖς νοσήματι ἀνηκέστῳ ἐξουσίαν λαβόντι μηδενὸς ὧν ἐπιθυμεῖ φείδεσθαι, ἀλλὰ τοῖς μὲν ἰατροῖς ἐῤῥῶσθαι φράσαντι, ἐκ δὲ τῶν ὀλέθρων ἐγειρόντων ἑαυτὸν ἐξωθοῦντι· τούτου ἕνεκα δύσκολός σοι ἡ ἐπάνοδος ἢ ἐπὶ τὴν σωφροσύνην δοκεῖ. Εἰ δὲ παύσοιο τῆς ἐρωτικῆς οἴστρου ἐκμαινούσης τρυφῆς (ῥίζα γὰρ ἀσελγείας αὕτη, καὶ μήτηρ καθέστηκε), σβεσθήσεται, καὶ ἡ τῆς ἀκολασίας φλόξ. Τῶν γὰρ ὅλων ὑπεξαιρεθεισῶν, καὶ τὸ ἐξ αὐτῶν αὐξόμενον, καὶ κορυφούμενον πῦρ δηλονότι ἀποσβεσθήσεται. Εἰ δ᾽ αὐτὸς τὰς ὅλας τῷ πυρὶ χορηγεῖς, πῶς λήξει καὶ παύσεται; Εἰ αὐτὸς ἠρεμοῦν διεγείρεις τὸ θηρίον, τίς αὐτὸ κυκῶν καὶ μαινόμενον τιθασσεύει; Ταῦτα οὖν καὶ τὰ τοῦτ᾽ ἀδελφὰ ἐννοῶν, παῦσαι τοῦ διὰ παντὸς τρυφῶν.