This is a philosophical proposition, that is, the two sides of the contradiction of things are mutually transformed. China's sages have long noticed the phenomenon that prosperity will decline, and the monthly surplus will be lost at night, and the water will overflow when it is full. If you divide it for a long time, you will divide it for a long time. In other words, as the saying goes, "people are kind for a hundred days, but flowers are not red for a thousand days", "thirty years in Hedong, thirty years in Hexi"; This is also the meaning of "good flowers don't bloom often, and good times don't last long" sung in popular songs.
Related philosophy
In astronomical phenomena, due to the changes in the relative positions of the moon, the earth and the sun, when we look at the moon from the earth, there will be changes in profit and loss or roundness. During the operation of the earth and the moon, the "moon phase" of the full moon we observed will gradually show the "moon phase" of the waning moon with the change of the relative positions of the moon, the sun and the earth.
Whether "full moon leads to loss" or "full water leads to overflow", according to a famous saying of China, "extremes meet". That is, the contradictory movement and change of things, from quantitative change to a certain extent, will lead to qualitative change, and contradictions will turn into opposites. The full moon will not remain unchanged forever, but will become a monthly loss; When the water is full, it will not stay for a long time, but will turn to overflow.