Concentrate on the subject or the act in question, on principle or meaning. You deserve what you're going through. You would rather become good tomorrow than be good today.
Doing something? I do it with reference to the benefit of mankind. Something happening to me? I accept it in reference to the gods and the universal source from which all things spring interrelated.
Just as you see your bath - all soap, sweat, grime, greasy water, the whole thing disgusting - so is every part of life and every object in it.
When you observe the totality of life, especially in the context of the vastness of time and space, life indeed is short. When viewed from this perspective, how puny it seems for someone to seek praise and to be remembered.
The only life you truly have is the one you have at this very moment. Therefore, concentrate on the subject or matter at hand. Marcus chided himself for wanting to become good tomorrow rather than being good today. I am guilty of this too. Carpe diem - seize the day! Do it now! Don't make plans to be better - be better!
With regard to action, always act with the purpose of benefiting others. With regard to something happening to you, accept it. A meeting location changed on you - if the change in location is not up for debate, then accept it and move on. But if you think you have control over changing the location again, by all means use your ability to think and act. Always view things in two buckets: things in your control and things out of your control. If anything that happens to you is out of your control, don't complain; pivot and move on.
Marcus really tries to suck all his desire for things out of his control. One of the ways he does this is to view the sum of life. In a sense, he's simply saying don't get attached to all the things in life. What happens in life is for your use in becoming better. And in that process, don't get so attached to life, health, wealth, fame, etc. Rather view life as a scrubbing. The materials and leftovers are disgusting, but the product (you) ought to be clean.
(see also Citadel p. 38-40, 45, 49, 164-165, 185, 270)