How did birthdays become gossip fortune telling?

The birth date can be changed into six hexagrams, and the number of months and days in the lunar calendar (year after year, such as the first year of the child and the second year of the ugly year) are all added up and divided by eight to take the remainder as the upper hexagram; All hours of the year, month and day are added and divided by eight, and the remainder is the next hexagram, and the remainder divided by six is a dynamic one.

Eight characters can be transformed into Heluo hexagrams, but that is more complicated, so I won't say it here. You can download Baidu search if you are interested, and then study it slowly.