As a not-even-really-observer casual observer, game 6 must have just broke him. Even in those rare moments where he had played to an advantage, he unforced-error-blundered it away mere moments later. There were at least two instances where Magnus was so stunned at the nature and plainness of the blunder that he had to collect himself in a "am I walking into a trap, you couldn't have just made that mistake" sort of way. Opening himself to that pawn fork... these weren't carefully laid traps he was falling into. This was shooting himself in the foot and face with Magnus out of the room. Absolutely stunning meltdown. I feel sorry for him, but mental endurance is obviously no small part of the calculus to being world champion and Nepo showed he simply doesn't have it.

Good mental is one of the core skills, and I think the silver lining for Nepo in this is that it’s very clear what he needs to improve. Hopefully he’ll be able to pick himself up and become a stronger competitor from it.

Incidentally the mental test of this best of 14 format isn’t even as hard as it can get. They used to play to a certain number of wins. The 1984 championship was abandoned in February 1985 (it started in September 1984) after 48 games (40 draws). They also had longer time controls back then, and would adjourn games overnight if necessary, so when you woke up to play a game you wouldn’t even know if you’d be able to go to sleep that night having finished it.

Do you really think Nepo would be at that level without mental endurance?

How else would you explain the moves well below his level that objectively cost him? He is a great player but does not have Magnus’ mental and emotional consistency. Not everyone advances to the top in chess with the same combination of inner traits. This is also seen in other competitions where humans must perform at their absolute best in all aspects to reliably win.

Saying Nepo has less mental endurance than Carlsen is not the same as saying he doesn't have any as this poster wrote.

Ah. I think the meaning was clearly relative to the level of play and you took it too literally.

That’s incorrect. The original poster said Nepo lacks the mental endurance required to be world champion, not that he lacks it altogether.

He lacks enough of it to become one at this point in time (when we have Magnus and Nepo has his current mental edurance) :)

Actually relative strength is one of the things that wonder me the most I would say in the game: when one of the opponents is much stronger than the other the wins look so easy and the loses so stupid, but when the winner is matched against someone even stronger you see the same exact picture. I love you all I dunno why I say that now but here you go.

Before the match, Carlsen said about Nepo:

“It remains to be seen, of course, if Ian will be more resilient than he has been in the past if he is down”

So yes, it seems he has a bit of a problem in that department.

(https://www.theguardian.com/sport/2021/nov/24/magnus-carlsen...)

It's interesting because this weakness of Nepo was known going into the championship. And I have to presume that he worked on it. But there was just not enough time to have him build up the necessary mental conditioning. I suspect if he had a year or two to prep, Ian would have done a lot better.