China's ancient philosophy holds that the two opposites of matter and personnel in the universe are "Yin and Yang". Things in nature include size, length, up and down, left and right, etc. The ancients divided it into big, long, upper and left yang, and small, short, lower and right yin. Yang is strong and yin is weak. Men are strong-willed and belong to yang and left; Women are gentle and belong to the yin and the right.
In addition, it is also related to the tradition that men are superior to women in China feudal society. From left to right, men come first, and men are just yang, ranking above women.