The “10,000 is things”expression for all that happens in a life, or in the world of our experience. They arise and pass away, continually rearranging themselves, and we have to learn how to work with this reality:
The ten thousand things arise together;
In their arising is their return.
Now they flower, and flowering sink homeward, returning to the root.
The return to the root is peace.
Peace: to accept what must be
and to know what endures.
In that knowledge is wisdom