This is the "golden mean"
It means that when things develop to the extreme, they must transform in the opposite direction, that is, when things reach their extreme, they must be reversed. He advises people to be modest and not complacent, to be measured and tactful in doing things, to leave room for leeway, not to go overboard, and to be low-key and pretend to be stupid when appropriate and necessary.
Because everything is a contradictory unity, with two contradictory aspects. When under certain conditions, a certain aspect of a contradiction dominates and plays a decisive role, things will take on the properties determined by it. But it also contains opposites, which will continue to accumulate and eventually dominate, making things go to the opposite side.
Explanation
When the moon is full and waning, the water overflows: when the moon is full, it wanes; when the moon is full, it overflows. It is a metaphor that when things develop to a certain extent, they will transform in the opposite direction.
Great wisdom and foolishness: People with high intelligence and talent do not show their sharpness and appear to be very stupid.
Chaos: Also known as "Chaos", the name of the central emperor in ancient fables. The original meaning is a metaphor that everything should be allowed to take its course. It is often used to express ignorance.
Cangming: the sea, the sky, the high and deep sky.
Youjian: a deep valley or mountain stream.