"Thirty years east of the river, thirty years west of the river" is a folk proverb, which comes from the natural phenomenon that the Yellow River often changed its course in history. In the past, the Yellow River was not fixed and often changed its course (it happened countless times in history). A place used to be on the east side of the river, but in a few years, due to the diversion of the Yellow River, this place will become on the west side of the river. This sentence is a metaphor for the ups and downs of personnel, which is changeable and sometimes becomes the opposite and unpredictable.
Related historical allusions:
Guo Ziyi's grandson had to beg after losing all his property. Once, he begged to visit his wet nurse in Hexi Village. I asked a lot of people and said I didn't know. It was getting dark when a farmer came. When he inquired, he found that the farmer was the son of his wet nurse. When he went to other people's homes, all he saw were grain shops and cattle and horses.
He asked the farmer, "Your family is so rich, why do you have to work by yourself?" The wet nurse's son said, "No matter how big the property is, it will be empty. When my mother was alive, she led us to start a business, and this family business came into being. It's fun to be diligent and keep a house! " Guo Sun felt ashamed after hearing this. The master never forgets the old love and lets Guo Sun manage the accounts at home, but he knows nothing about accounting. The master couldn't help but sigh: "Indeed, in thirty years, Hedong enjoyed endless prosperity, and in forty years, Hexi relied on the old to sell the old."