Why did the ancients advocate nine and multiples of nine like that?

Nine in ancient times was considered as the largest number.

1 and "nine" are the largest of these figures, the high-end of rights and the most respected. In ancient times, it was used to describe the status of the emperor, such as "the respect of the ninth five-year plan", and even officials had to "worship three times and knock nine times"

It is also said that the word "nine" evolved from the dragon (or snake) totem, so this word has the same sacred color as the dragon, so the ancients used it to compare kings. Of course, the king wants to be associated with it.

2. The ancients took "nine" as a large number, so there was a saying that "nine-nine returns to one" or "nine-nine returns to the original". Sometimes used to express the limit, such as talent has nine layers, the highest is "nine layers of heaven", which refers to the extremely high sky. This idiom is like "outside the cloud nine"

Hope to adopt ~