He was harder to break mentally, he took a beating because he sucks at striking and Carwin had good tdd. He broke so quickly against Cain and against Overeem he just didn't care at all, he was beaten before he even stepped in the octagon. It's the difference between when a fighter only loses if the other guy breaks him physically or when a fighter will beat himself, losing his sense of physical superiority took away all his confidence because he always knew he couldn't strike at all. Happens in every sport, take Rene Bourque for example, he was a wrecking machine of a hockey player, got injured, became a timid wuss that would shy away from guys half his size. The Brock that went in against Mir and Herring went in with fire, the Brock that fought Cain was unsure and the Brock that fought Overeem had a 0% chance of winning. It's like when a guy blows out his knee and he's always weary of going all out even if it does fully heal.
I'm not even blaming Brock, getting sick like that would end most people's athletic career.
Okay, maybe getting smashed against Carwin hurt his ego, but that's still the fighter that's ego was hurt. He's the same fighter against Overeem and against Mir. Those striking insecurities were always there, he just had to get punched to feel them. I dont think his sickness was anything to do with his last two fights. To be fair, they were against two of the best heavyweights ever, both killer strikers, and he didnt stand a chance going in really.
Which is correct is that Lesnar didn't fight back in both fights, so the referee could have stopped the fight against Carwin. But actually there was a difference: Because of Carwins stupidity, most of his shots landed on Lesnar's forearms. So Lesnar didn't get that hurt. In contrast, Velasquez picked his shots and really hurt Lesnar.
So against Carwin the fetal position was the result of timidity, against Velaasquez it was because of real damage.
Concerning the discussion whether you can learn how to take a punch and how to react on it, according to my observations over the years in the gyms, actually both parties where somewhat right. Yes, you can train to take a punch and to get rid of your timidity, BUT only to some extend. There are people who react better to pressure than other people, and they always will if they have comparable training. I'm not sure whether it's purely genetically or early childhood imprinting, but usually after less than a year of hard sparring you can see whether someone has that "never give up"-spirit under pressure or whether he hasn't. It's the same as in every other aspect of things to train. You can train to run and you will run faster, but only few people can get to Olympic level. And to stay at an elite level of MMA, you have to be one of those guys genetically gifted/correctly imprinted in early childhood at reacting to be under pressure. And Lesnar doesn't seem to be one of those, after his illness even less.
Yeah Velasquez finishes fights much better than Carwin. The referee could have stopped it but I have always been in Brock's corner with it. He was HATED at the time (well in non MMA site dicussions) and I sort of liked him. I defended him before it and when people said "They'd have ended it with anyone else, this is corrupt" I was thinking "He was able to come back and win the fight, he defended well enough that means". No chance with Cain.
Your last part wasnt really what we were talking about, but I agree with all of it.