Seneca, Moral Epistle 53. 9-10
“If you were sick, you would break from personal affairs and neglect your work responsibilities—you would not care enough for an client to work on his case during a brief respite from illness. No, you would work with all your mind to free yourself from sickness as soon as possible.
What then? Won’t you do the same thing now? Dismiss all obstacles and dedicate yourself to a healthy mind. No one who is distracted can achieve this. Philosophy rules her own realm: she makes the time and does not accept appointments. She is not a random assignment but a regular obligation. She is master: she is here and commands.
Alexander, to a certain state who promised him half of their possessions and lands, said “I came into Asia not with the plan of me taking what you offered but for you to have whatever I left behind.” In the same way, philosophy says to all other affairs: “I am not going to accept the time you don’t need, but you may have the time I don’t take.”
Si aeger esses, curam intermisisses rei familiaris et forensia tibi negotia excidissent nec quemquam tanti putares cui advocatus in remissione descenderes; toto animo id ageres ut quam primum morbo liberareris. Quid ergo? non et nunc idem facies? omnia impedimenta dimitte et vaca bonae menti: nemo ad illam pervenit occupatus. Exercet philosophia regnum suum; dat tempus, non accipit; non est res subsiciva; ordinaria est, domina est, adest et iubet.  Alexander cuidam civitati partem agrorum et dimidium rerum omnium promittenti ‘eo’ inquit ‘proposito in Asiam veni, ut non id acciperem quod dedissetis, sed ut id haberetis quod reliquissem’. Idem philosophia rebus omnibus: ‘non sum hoc tempus acceptura quod vobis superfuerit, sed id vos habebitis quod ipsa reiecero’.
This reminds me of a passage from Epictetus:
Epictetus, Treatises Collected by Arrian, 2.15: To those who cling to any judgments they have made tenaciously (Available in translation and Greek on the Scaife Viewer)
“Whenever some people hear these words—that it is right to be consistent, that the moral person is free by nature and never compelled, while everything else may be hindered, forced, enslaved, subjected to others—they imagine that it is right that they maintain every judgment they have made without compromising at all.
But the first issue is that the judgment should be a good one. For, if I wish to maintain the state of my body, it should be when it is healthy, well-exercised. If you show me that you have the tone of a crazy person and brag about it, I will say ‘Dude, look for a therapist. This is not health, but sickness.’ “
ιε′. Πρὸς τοὺς σκληρῶς τισιν ὧν ἔκριναν ἐμμένοντας.
῞Οταν ἀκούσωσί τινες τούτων τῶν λόγων, ὅτι βέβαιον εἶναι δεῖ καὶ ἡ μὲν προαίρεσις ἐλεύθερον φύσει καὶ ἀνανάγκαστον, τὰ δ’ ἄλλα κωλυτά, ἀναγκαστά, δοῦλα, ἀλλότρια, φαντάζονται ὅτι δεῖ παντὶ τῷ κριθέντι ὑπ’ αὐτῶν ἀπαραβάτως ἐμμένειν. ἀλλὰ πρῶτον ὑγιὲς εἶναι δεῖ τὸ κεκριμένον. θέλω γὰρ εἶναι τόνους ἐν σώματι, ἀλλ’ ὡς ὑγιαίνοντι, ὡς ἀθλοῦντι· ἂν δέ μοι φρενιτικοῦ τόνους ἔχων ἐνδεικνύῃ[ς] καὶ ἀλαζονεύῃ ἐπ’ αὐτοῖς, ἐρῶ σοι ὅτι ‘ἄνθρωπε, ζήτει τὸν θεραπεύσοντα. τοῦτο οὐκ εἰσὶ τόνοι, ἀλλ’ ἀτονία’.