Birthday horoscopes, or eight characters, are actually another way of saying the four pillars in the Zhouyi terminology. The four pillars refer to the time of birth, namely year, month, day and hour. Humans use one word each for heavenly stems and earthly branches to express year, month, day and time, such as Jiazi year, Bingshen month, Xinchou day, Renyin time, etc. Each column has two characters, and four columns have eight characters, so fortune telling is also called "testing eight characters". According to the relationship between the heavenly stems, earthly branches, yin and yang and the five elements' attributes, we can speculate on people's misfortunes and blessings.