The “10, 000 things” is a shorthand way of talking about all the experiences –  good and bad – which arise and pass away in our lifetime, continually in movement, with ebbs and flows.  Eastern wisdom considered that they  contain the right mix of experiences for our growth.

When the 10,000 things become one,
then we return to the center,
where we have always been.

Chuang-Tse, Chinese philosopher, 4th century BC