The reason why people were barred from taking the civil service exams for up to three generations during the Joseon Dynasty

In the early Joseon period, most people were able to take the civil service exams.
Slaves accounted for only 5%, while 95%—the nobility (Yangban) and commoners (Yangmin)—were eligible.
The child of a concubine of a nobleman was a "Seoja," and the child of a noble and a slave was "Cheonchul" (lowborn);
Joseon was a nation that followed the "Jongmo-beop" law, meaning status was determined by the mother.
Even for such lowborn slaves, taking the military service exam (Mugwa) was permitted.
As a result, several individuals rose to the rank of Dangsang-gwan (Senior 3rd rank or higher).
Despite being a nobleman, Admiral Yi Sun-sin's father was ineligible to take the exams.
This was because Yi Sun-sin's great-grandfather was unfairly implicated and punished during the Muo Literati Purge.
As her husband fell into despair and lived idly, his wife, Lady Byeon (Sun-sin's mother), could no longer endure it;
she settled their affairs in Hanyang and moved with her children to her hometown, Onyang.
Originally, Yi Sun-sin's hometown and the place where he spent his childhood was Geoncheon-dong, Hanyang.
It is near the current Chungmuro in Jung-gu, and it is a fascinating coincidence that his neighbors were
Ryu Seong-ryong and Won Gyun.
In Asan, Yi Sun-sin gets married.
He became the disciple and son-in-law of Bang Jin, a former magistrate from a military background,
and it was at this time that Sun-sin switched his exam track from the civil service (Mun-gwa) to the military service (Mu-gwa).
Contrary to the title, the story has drifted quite far.
This was because the royal court believed that ideological teachings and grudges could persist for up to three generations.
This was also stipulated in Jeong Do-jeon's ideologies and the Gyeongguk Daejeon (National Code).
While there was some logic to it, there must have been many scholars who suffered unfairly.
I think quite happily that perhaps the misfortunes of his ancestors led Sun-sin to become the Commander of the Naval Forces,
ultimately saving all our ancestors...