A lot of people put themselves into danger every day, frequently in completely voluntary activities like mountain climbing. Or a husband giving their wife an unbiased opinion when asked how they look. Truly terrifying.
Sure, absolutely. And sometimes, they freeze up or hide or otherwise flinch or hesitate when they never have before. This stuff happens. The mind is powerful, and fear and other emotions can be powerful. They also influence us physically... so it's not purely mental or emotional as you're saying.
Mundane conversations are also rife with examples of this stuff. There are many times where my emotions got the better of me in dealing with my wife or one of my kids, or other family and friends. Sometimes, we get angry or hurt, and then we blurt something that we immediately know was bad... but that happens.
Sometimes, in some games, I really like this kind of phenomenon to be on the table.
What's contradictory? I give the players information I think the characters should have.
Here's what you said:
The GM doesn't choose to withhold information. They decide what information the characters should reasonably have.
If the GM is deciding what information the characters should reasonably have, then they're also deciding what information they shouldn't have. Which is withholding information.
I could, and frequently do. I think things like holy symbols for the major religions is common knowledge. You need fire to kill trolls, vampires don't like sunlight, any number of things are common knowledge.
Sure, but those are relatively easy to justify. There are many other examples that have come up that the GM could simply provide, but folks are saying should not be.
If I'm envisioning something about things about the environment it's going to be dependent on multiple things. Am I describing something based on a place I've been and have personal experience with or have read about? What makes sense for the current scenario? A well maintained castle wall is going to be very difficult or impossible to climb by design. Other times it's just a judgement call on what's going to be the most fun for the group.
Can it be arbitrary? Sure. I don't care. It's what I think either fits what I've envisioned or will be a fun challenge. Sometimes that means they scrabble up without difficulty other times they have to work a little harder to figure out alternatives or take a chance.
But it sure seems you're trying really hard to conflate "I think it's realistic that you don't always know how easy it is to climb a cliff" with a gotcha "Aha! So it's not based on a real world cliff!"
No, I'm not deploying a gotcha. I'm being very direct. I'm saying that whether or not the cliff is visibly easy to climb, or rather that the difficulty of the climb is not subject to hidden information... is up to the GM.
If a GM chooses to say that there is hidden information that is a factor, then that's a choice. It impacts play and it's on the GM. It's not something that's happening "because realism".