A device named as another's, but taken as one's own. Marcus records not a thought but an instruction (παράγγελμα — a word from medical and military usage: "an order, a direction"), and notes where it comes from1. He does the same with the Pythagoreans (11.27): the neighbouring passages collect other people's practices, serviceable whatever the school.
What exactly is prescribed. EXERCISEσυνεχῶς ὑπομιμνῄσκεσθαι — "continually to remind oneself" (not "to reflect," not "to imitate"): the same verb that stands at 11.6 of tragedies brought on ὑπομνηστικαί. And the object: τῶν παλαιῶν τινος τῶν TERMἀρετῇ χρησαμένων — "some one of the ancients who made use of virtue." Χράομαι ("to use") rather than ἔχω ("to have"): virtue here is not a property possessed but a tool put to work.
Why "some one." τινος is indefinite: neither a model nor a canon is appointed. What matters is not the figure but that there be a figure: an abstract notion of virtue does not work as a reminder, whereas a person known to have done it does.
Where this has already been done. The whole of Book I is this precept carried out at length: a catalogue of persons and of what Marcus learned from each. And the nearest instance is the neighbouring 11.28, recalling Socrates in the sheepskin. Cf. also 6.48: when you wish to gladden yourself, think of the excellences of those you live with. The governing discipline is assent, the sustaining one action.