Why is it' seven ups and eight downs' instead of' eight ups and seven downs'

In the divination of the Book of Changes, there will be four divination numbers of 6, 7, 8 and 9. Among them, the even numbers of 6 and 8 are yin, and the odd numbers of 7 and 9 are yang; And 7 and 8 belong to the same, because 7 rises to 9, or it belongs to Yang; Eight is yin, which can be returned to six, and it is still yin, so there are seven cases.

In addition, the numbers 9 and 6 belong to the change of mind, which coincides with the yin of the anode and the yang of the cathode, while the Yijing divination just takes the change of mind. . . Don't start talking.