I think symbolizes the emotional scar he left on them, with how he treated them roughly and aggressively and how he pushed them to the point of breaking them for the sake of polishing them
Even the professor himself has a scar
Not the same one as his students
what I was trying to say is that he himself had suffered trying to be perfect,of course that doesn’t excuse him for being a douche
Why all heejae's students have a cut of their face ong