You probably want to talk about the Book of Changes, but the main function of the Book of Changes is not to look at a person’s birthday and horoscope. The Book of Changes talks about yin and yang, and the eight characters focus on the five elements. In fact, the two originally belonged to different systems. However, later generations integrated the fortune-telling theory into yin and yang on the basis of the five elements, and gradually evolved into the commonly used four-pillar and eight-character fortune-telling techniques.