Why do you have to take out one of the 50 hexagrams before you take it?

In ancient times, the method of divination with yarrow was very complicated; For example, the copula says, "The number of big swallows is fifty, and nine out of forty are used; Divide into two, with two elephants, hang one with three elephants, rub it with four, with four elephants, return to singularity, jump like an elephant, and then jump at the age of five, so hang it again. This is the divination method of yarrow.

Take one of 50 yarrow trees and put it in the upper part of the middle of the table as Tai Chi.