A nat 20 is the best outcome that the character could manage in that situation, if they have no chance of succeeding then the DM should not be letting them roll. If the barbarian suggests mauling a delicate machine with their mace it’s down to anyone else in the party (or the DM if they’re so inclined) to remind them that actions have consequences.

Of course nothing should be inflexible, but I’m just saying there’s no reason for every campaign to be derailed completely. If your players are actively going against the scenario something’s gone wrong. And yeah, if you give them the opportunity to do something, be prepared for it to happen and roll with the consequences.

Unless you play low level John Does every time, characters should know stuff about the world they’ve lived in their whole lives. And if none of that ties into the scenario are you playing a campaign or in a sandbox?

If everyone’s on the same page and wanting to play out a story, seeing how your characters and world changes in response to things not playing out as expected is part of the fun. It should never truly derail unless someone is trying intentionally to, in which case you need to talk about it. Or you got complacent and dangled a campaign altering thing too close for them to resist…

This is similar to what Rick Riordan (author of Percy Jackson) suggests in one of his other works - that the afterlife is simply whatever you believe it to be. It’s pretty comforting imo.