Open Question: How precise and quick is a Grand master in Karate?

How precise and quick is a Grand master in Karate? Like you always see these movies where they can can do all this neat crap and are almost untouchable by anyone even a rank lower then them. Is this true or just movie fiction? We’ve been hanging out with someone who is a 3rd Degree black belt, and he said his master could break a bottle over his head and jump up and down on the broken glass without injuring himself at all… How the f**** is that possible?