One question instead of a complaint. The passage opens with a working formula: τί ἐστι τὸ ἐπὶ ταύτης τῆς ὕλης δυνάμενον κατὰ τὸ ὑγιέστατον πραχθῆναι; — "what, upon this material, can be done or said in the soundest way?" Two words carry everything: ὕλη turns the circumstance into raw stock, and the superlative ὑγιέστατον sets the measure — not "rightly" but "most healthily." And at once the cutting-off of excuses: DOGMAμὴ προφασίζου ὡς κωλυόμενος — "do not plead that you are hindered."
Enjoyment redefined. The second paragraph strikes at the root of complaint: you will not stop groaning until acting according to your own constitution becomes to you what τρυφή (luxury, indulgence) is to those who live for pleasure. And the conclusion is framed as an instruction to judgement: ἀπόλαυσιν δεῖ ὑπολαμβάνειν — one must reckon as enjoyment everything one may do TERMaccording to one's own nature. Not "give up enjoyment," but "transfer the name to something else."
Cylinder, water, fire. The central argument is a comparison with the irrational. To a cylinder, to water, to fire, their own motion is given not everywhere: many things "fence them in and stand in the way" (τὰ διείργοντα καὶ ἐνιστάμενα πολλά). But TERMνοῦς and TERMλόγος DOGMApass DOGMAthrough everything that resistsDOGMA (διὰ παντὸς τοῦ ἀντιπίπτοντος) — as they are framed by nature and as they will. The difference is not one of strength but of topology: a physical body needs a clear path, reason does not.
And at once the image is inverted. ταύτην τὴν ῥᾳστώνην — "this ease" — keep before your eyes: reason will be borne through everything "as fire upward, a stone downward, a cylinder down a slope." A moment ago the cylinder was the example of limitation; now the same cylinder is the image of natural irresistibility. Marcus takes the identical trio and turns it through 180°.
Why an obstacle does no harm. The remaining ἐγκόμματα (hindrances) either concern "the poor body, which is a corpse," or else — TERM"apart from ὑπόληψις" and without reason's own yielding — they neither crush nor do any TERMharm whatever. The proof is by reductio: otherwise the sufferer would immediately become bad, and that does not happen. On the contrary: in every other construction harm makes the thing worse, whereas a man, by using rightly what befalls him, becomes better and more praiseworthy. Cf. 5.20 (the obstacle to action advances the action); 8.32.
The closure through the city. The end is a chain of three links: DOGMAnothing harms the citizen that does not harm the city; nothing harms the city that does not harm the law; DOGMAand of these "so-called misfortunes" not one harms the law — therefore neither city nor citizen. Personal invulnerability is derived not from fortitude but from the constitution of the polis: you take no harm because the law takes none. The governing discipline is action, the sustaining one assent.