I have never read such a short post where the poster was 100% right and 100% wrong at the same time. Its kind of interesting, actually.
I also think it has something to do with how tough you are mentally and physically.
Barring injuries, I'd say it has a lot more to do with mental toughness than physical. Having the mental capacity to push through shock, pain, and fear is essential to heavy contact fighting. Physical fitness and conditioning cannot be overstated but the mental abililty to remain calm and in control inspite of adrenaline, pain, and the fear of injury is what seperates a good heavy to full contact fighter from the rest.
Only the toughest can survive in full contact.
How do you measure that?
There are tons of boxing and mma gyms that prove otherwise. Kyokushin, as noted upthread, has students competing at
effectively all skill levels at full contacts. The Kajukenbo guys bang hard as well. If only the toughedt survive where are all of the deaths?
All joking aside, the prevalent myths associated with the deadliness of martial arts techniques, the lethality of a black belt, and the toughness of full contact fighters are a bit overblown. Heavy to full contact fighting will teach you timing, endurance, how to handle a hit, and how to deliver effective techniques against a fully resisting opponent. Is it the same as a street fight? Hell, no. It as accurate as a simulation as one is going to get with any level of safety.
Point work is better than not sparring, but I'll take heavy contact any day of the week.
I'm not among the toughest, but I survived just fine.
Mark