I find it a very strange thing.
You have Diego Sanchez, like many fighters had a great chin when they were young, then it suddenly just “went” and that was it.
Jake LaMotta has probably one of the greatest chins in history. He took damage throughout his entire career and still lived until 95 without pugilistic dementia.
Then you have someone like Overeem, who has always had a weak chin, been knocked cold too many times to count, yet his faculties are still there.
Any kind of brain trauma is bad, but I guess you never really know if you’re one of those who drew the short end of the stick genetically. I’m glad I’m not a fighter.