Think about it, how to write the word "eight"? The first one is "hmm", and the first one is not written. How can there be a complete "eight"?
At first, people used "eight characters not left" to describe the marriage between men and women. "Eight characters" refers to the date of birth of men and women. In ancient times, the birthdays of both men and women had to be together (that is, not contradictory) before they could get married.
In the old days, there was a common name "send eight characters", which meant formal engagement. First of all, parents of both men and women ask fortune tellers for their wedding birthdays. If the constellations match, the man chooses his birthday, and the man exchanges parties with the woman on an auspicious day, commonly known as "sending constellations".