What days does "Fat Day" refer to?

Explain the general statement one by one, this is a bit complicated:

Description: Fat day and thin day are opposites, and they are another name for "sunny day" and "cloudy day" in folk customs. Because the yang is full of yen, while the yin is like a lack of moon, which is the so-called sunny circle. Its correct name is combining rigidity with softness. The Book of Rites says that "diplomacy should be rigid and internal affairs should be soft." The idiom "external rigidity and internal softness" also comes from this combination of rigidity and softness.

Proof: Zeng Guofan once said that "the classics should be read every day, and the history should be read every day", and the combination of rigidity and softness is a metaphor of yin and yang, that is, balance and harmony. There is also a popular saying that reading classics on sunny days and reading history on cloudy days ... In addition, odd days are regarded as yang and even days as yin, which is a fortune-telling rhetoric.

Commentary: For fortune telling, different daily life or work needs 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 ... you must have a fat day to kill pigs (see the article "The Eight Characters of the Fortune Teller").

Conclusion: As a scholar, just look at the first words of every day in the lunar calendar (such as Wu Zi), namely A, C, E, G and Ren Wuqi (see Book of Rites Justice, "The fifteenth day is strange, and five couples ... are foreign affairs, so the righteous day is also used"). But for old fortune tellers and witches, this calculation is more complicated, because it is what they rely on to make a living. This calculation method involves the Book of Changes and other contents, such as detailed star worship? It will involve different religious beliefs and individual differences, and it is more likely to involve the calculation of earthly branches, not just heavenly stems. Therefore, a certain day of a certain year will be a good day for someone to get married. Miss this day, is it a small fortune or a big disaster, or how long it will take to hold the wedding. It's just that this is somewhat puzzling, and there is no actual example to prove the correctness of the calculation.

(I suddenly thought of the video of Meituan's little brother: yellow robe plus body, big fish and big meat ...)