Two things that must not be knocked out of you, not one. The passage is built on a parallel: as the obstructors will not turn you from sound action (ὑγιὴς πρᾶξις), so DOGMAlet them not knock out your DOGMAgoodwillDOGMA toward those obstructors either. The verb ἐκκρούω is "to knock out by a blow"; Marcus treats another's pressure as a shove that can dislodge you from two different positions. The usual Stoic formula defends one — the rightness of the act; here both positions are put under guard, and the second is named as the equal of the first.
A symmetrical watch. EXERCISEφύλασσε σεαυτὸν ἐπ’ ἀμφοτέρων EXERCISEὁμοίως — "guard yourself on both alike": not only on εὐσταθὴς κρίσις καὶ πρᾶξις ("steady judgement and action") but on πρᾳότης — mildness toward those who try to hinder "or are otherwise put out." Πρᾳότης here is not softness of temperament but the working virtue toward the one who obstructs.
Anger is named a weakness, not a sin. καὶ γὰρ τοῦτο ἀσθενές, τὸ χαλεπαίνειν αὐτοῖς — "for this too is feeble, to be harsh with them." A diagnosis, not a condemnation: irritation is set in one row with fright. Both are ἀσθένεια; only the direction differs.
The military metaphor levels the two failures. ἀμφότεροι γὰρ ἐπίσης λειποτάκται — "both alike are deserters" (λειποτάκτης, one who has left the ranks; in Roman law the gravest military offence). The one ὑποτρέσας — "having flinched"; the other TERMἀλλοτριωθεὶς πρὸς τὸν φύσει TERMσυγγενῆ καὶ φίλον — "having become a stranger to one who is by nature kin and friend." The move is severe: to be embittered at an obstructor is equated with running from the field. And the ground is not magnanimity but a fact of kinship: the one who hinders remains συγγενής all the same.
A note on the ranks. The word λειποτάκτης stands next to 11.8 by no accident: there the one who separates cuts himself off from the community, here he takes himself off his post. Two figures of falling away in succession, the botanical and the military. The governing discipline is action, the sustaining one assent.