It’s about Jooins past!
Spoilers
So Jooins mom died when he was young. He got a new stepmom but his dad was always at work and she’s being in people to gamble and stuff. She also started using Jooin because she was the first to notice his rlly good memory. Time skip to when they were at court, Jooin revealed all that she did and she started calling him a creepy person. she said that he was different and that he had no heart. This really affected Jooin to creating fake personas to not reveal who he is. Ji-ho tríes to talk to him but each time he fails saying how Jooin has a some kind of “defense system”. Jooin also hates his memory. Jiho’s exact quote was “In some way, you are the only person whom Woo Jooin saved with his superb memory that he loathes.” (He was talking to Donnie)

As a novel reader... Eun Ji-ho seems like the better male lead.
Jooin I can’t look at him the same way without being a lil heartbroken
And 이루다 <33