What happened to ponds and rivers after many years?

The change of pools and rivers after many years is that the pools have dried up. The six lines of this poem are as follows:

Sure enough, the words of the river came true, and the river kept flowing from now on, but the poor pool was silted up year after year, covered with moss and reeds, and finally dried up completely.

By describing the different views and attitudes of ponds and rivers towards life and their different endings, the text tells us not to covet comfort, but to make more contributions to society.