beta
I wonder if another potential reason for the backstory is to show the duality of JJK and Kim Dan. IK some think its some sort of excuse for JJK's behavior, and while it does explain how anal he can be about success, it doesn't excuse his actions. But maybe the author included it to show two different approaches to financial poverty.
Like with JJK, his aggression and drive got him out of a difficult situation, but he lost some of his humanity along the way. Kim Dan stayed a kind sensitive soul, but struggled to maintain emotional boundaries and garner finances.
This is probs me just reading too much into it, but its an interesting way to look at how these two approached their financial circumstances. In a way, they both had to 'sell' themselves. JJK to physicial violence, and Kim Dan to sexual aggression.