UFC is a lot more than just knuckle heads fighting it out. It takes a lot of thinking to get thru a round.
Some of those guys can tie others up so fast, they won't know what happened! So, it's up to the challenger to be constantly thinking, of not only the current situation, but three moves after that one has failed.
I ain't saying I'm any expert by any means, but I can say from experience that it's probably one of the most demanding sports, physically and mentally, that I've every competed in!