
Actually, his jinx is a routine that he had to adopt to ease his mind from trauma to perform better at a match. All of this was to forget about his father and all the trauma he suffers from, hence why, before a match, he drinks milk (which he used to steal and was most likely precious to him), makes sure to be clean (he got bullied by other kids for that) and has sex (it's stimulating and apparently works great against the nightmares he has about his father). When you say the reason of his jinx is stupid, I have to disagree because his jinx actually includes all the other traumas I mentioned before. It just so happens that sex is effective on him.

Yes, I like how realistic it is. It depicts well how trauma can affect someone, no matter how strong-willed they might be. JK is the best athlete because he was always so determined to change his life. But his traumatic past was a challenge for him, which is why, until he found his jinx, he was haunted by his fears. Mingwa made the character more interesting that way ^^
so what, he got this jinx just because he lost few matches when he was young? Thats stupid