From what it’s explained pretty much just because he came out resembling his brother. And his brother is waaayyyy waayyyyyyy more successful than he ever will be. So he hates him I’m guessing just on that. Cause he had a fucking inferiority complete towards his brother with money and looking at his little boy reminded him of his brother. Until the younger one was born and looked like him with his stupid hair.

Has there ever been any explicit details about why Cheol's dad hates him? It's kind of odd that it started when Cheol was very young so I wondered if maybe he thought Cheol wasn't his son or something.