What is the meaning of Ten Years East of the River Ten Years West of the River Ten Years East of the River Explanation and Source

1, Ten Years Hedong, Ten Years Hesi, Chinese idiom, pronounced shí nián hé dōnɡ, shí nián hé xī, means flourishing and declining.

2, source: You Wanhou laughed sarcastically, hummed twice, and said, "Ten years of river east, ten years of river west," there is no sky that is not clear, and there is no moon that is not missing. (Wang Yulong's "Clear Spring Song")