What does the iron mirror mean by grinding the full moon again?

"In the middle stage, the iron mirror is reground, and the moon is full" is a fortune-telling term, which means that people may encounter some setbacks and difficulties in middle age, but just like the rusty iron mirror is reground, after hard work and experience, life will regain its vitality and reach the peak of life, just like the bright moon. This sentence is a metaphor for staying alert on the road of life, constantly honing yourself and making yourself stronger and more determined.