Meditations 12.3:

If you can cut yourself—your mind—free of what other people do and say, of what you’ve said or done, of the things that you’re afraid will happen, the impositions of the body that contains you and the breath within, and what the whirling chaos sweeps in from outside, so that the mind is freed from fate, brought to clarity, and lives life on its own recognizance—doing what’s right, accepting what happens, and speaking the truth—
If you can cut free of impressions that cling to the mind, free of the future and the past—can make yourself, as Empedocles says, “a sphere rejoicing in its perfect stillness,” and concentrate on living what can be lived (which means the present) … then you can spend the time you have left in tranquillity. And in kindness. And at peace with the spirit within you.

“…doing what’s right, accepting what happens, and speaking the truth.” Simple and clear, if not easy.

Marcus keeps reminding himself that life is in the present. See through the illusion of past and future and just do what’s right, right now.