My MMA attempts have been some Karate in Middle School, some Krav Mega classes back in high school, and now some rolls around the mat at the BJJ school here, but I never really got into it or Wrestling. I respect the hell out of the people who do it though.
What I like most about MMA is once again (like hockey), the control of emotions while "performing". If you get too much adrenaline, you end up tiring yourself out. If you don't train endurance enough, you will lose. If you don't know how to control your breath, stay patient, and/or don't know how to / scared of getting punched... you will lose.
Playing chess and not checkers is important in all sports, but especially when you are in MMA. You have to know and predict your "partners" next move like a dance partner. Flow is what you would call it.
Anyways, I thought this was a great category to add to Sports and hopefully can get the experts to tell us more about how they train, think, etc.