I think it was already mentioned? Or was it my assumption? But something along the lines that his sis died and the trauma from that maybe? Idk something like that?
he wants to revenge on the bullies of his sister
So the actual reason was he became a doctor so tht he could earn ton of money for his sister (she is her only family and meant everythin) so tht her sister can lead a easy nice life. He held tht responsibility by himself and studied day night for it. After his sister's death. He felt tht ther was no need to hold for such position if his sister isn't with her anymore. Went depressed and choose wrong path following the traumatic experience. Sadge:(
I wanna know how he turned from being a doctor to being a thug lol