What is a birthday? What is this for?

Birthday, or eight characters, is actually another way of saying the four pillars of Zhouyi. Four pillars refer to the time when a person was born, that is, year, month, day and hour. When people use "heavenly stem" and "earthly branch" to represent year, month, day and hour respectively, such as Jiazi Year, Shen Bingyue, Xin Ugly Day and Renyin Time. There are two words in each column and eight characters in four columns, so fortune telling is also called "measuring eight characters" According to the relationship between yin and yang attributes and the five elements of heaven and earth, it is inferred that human body is responsible and blessed.