This passage comes from Professor Ceng Shiqiang's quotation about Chinese studies: Men are afraid of nine and women are afraid of six. Men are afraid of nine, because Yang is called nine at the extreme, and nine is the anode. Women are afraid of six, because six is the cathode number, the old yin, the pole number in the yin, and the movement becomes the yang number. In the face of nature, we'd better conform to it. When we meet 9 or 6 years old, we should pay attention to keeping in good health and conditioning our bodies.