This meditation is interesting to me. I had to think about it for a while.
6: From Marcus (Aurelius) I learned who Heraclitus was (Marcus quotes him a lot). “No man steps in the same river twice,” is one of the lines he quotes.
There are different ways to interpret this idea. In my brain, this river is your subjective experience of an event. In the first interpretation: the difference in time means that the river is never exactly the same. The second interpretation: the act of stepping into the river (or the event) changes the river and the conditions of the experience.
If you've ever read a book, the second or third time, you may understand it more, or you may find hidden meanings, or the book may now be boring. All of these depend on your viewpoint. The book doesn't change, but your subjective experience of it does.
I like this idea.