Description: Fat day and thin day are opposites, which is another name for "sunny day" and "cloudy day" in folk appellation. Because the yang is full of yen, while the yin is like a lack of moon, which is the so-called sunny circle.
Proof: Zeng Guofan once said that "read the classics of Japan and read the history of Japan", which is a metaphor for Yin and Yang. There is also a popular saying that reading classics on sunny days and reading history on cloudy days ... among them, odd days are considered as yang and even days are considered as yin.
Commentary: Yang/Gang/Non-Sun all refer to Yang in Yi. Later, it evolved into geomantic omen, and became a method to calculate yang dryness and yin dryness. (Some people in modern times will count it backwards, and yang dryness is yin pulp ...)
Difference: In different daily life, we need to calculate different yang dryness and yin dryness, that is, fat days and thin days. For example, the Six Livestock Fattening Day, that is to say, is suitable for building livestock pens. Similarly ... killing pigs is bound to be fat one day ... (see the article "The Eight Characters of Fortune Tellers")
Conclusion: Fat days are not fixed days, but good days calculated under different comprehensive conditions such as life/work/life (this is also one of the main reasons why witches in the old days were supported by villages and lived a carefree life). But as a scholar ... you only need to look at the single and double days to be fat and thin.
Reprinted. Hope to adopt