Why is philosophy seventy-two changes?

Wu Cheng'en is a master of Confucianism, Buddhism and Taoism. In The Journey to the West, he wrote China's philosophy into this wonderful article perfectly. The seventy-two changes in the Monkey King actually refer to the seventy-two changes in the ancient calendar.

The ancients took five days as days, three days as qi, six days as hours, four years as years, twenty-four solar terms a year, and seventy-two days. (First seen in Yi's Explanations of Zhou Shushi).

Among the 72 phases, each phase corresponds to a phenological phenomenon called "afterimage", which is also a change.

Journey to the West's writing about the Monkey King's seventy-two changes refers to the change, migration and circulation of all phenomena in the world, such as geography and astronomy, which is the so-called "way of nature".