He was born in a noble family but a clan that was framed for treason, so since he had little hope to rise in higher place or get a good post, he decided to try his luck on the military. Unfortunatly during the military exam he fell on his horse and broke his leg badly. Despite pulling himself, fixing his leg with branches and completing the exam he ended up failing. It was only after 4 years at his age of 32 with a new try that he managed to succeed the exam and got a post on the military.
However for him being in the army was somehow even harsher than getting there, as he got framed by someone for refusing a bribery, framed and almost got executed cause his officer blamed him for a jurchen raid attack despite Yi kept warning about an incoming attack. Thanks to his reputation he managed to avoid harsh punishment and gain his honor by participating in a campaign againts the jurchen. He decided to retire, and during those time he recall being disappointed in himself for not living up to his expectations he once had. One day a military officer asked him to return knowing his reputations and skills, Yi Sunsin decided to maybe give one more try and was appointed in the navy.
1592 Toyotomi Hideyoshi invaded Joseon/Korea and this event will soon completly shape Yi Sunsin...
I just wanted to give a little shout out to Korea's GOAT.