Sure, every other book written and movie created these days relies on the multiverse. If the character KNEW he was a character in a book it would be completely logical for them to think “Yep, I’m in an alternate universe.” In real life, though, that’s not a thing. If a character trips and falls into an alternate universe and thinks “Oops! I’ve always worried about this!”, It better be a comedy.
Sure, every other book written and movie created these days relies on the multiverse. If the character KNEW he was a character in a book it would be completely logical for them to think “Yep, I’m in an alternate universe.” In real life, though, that’s not a thing. If a character trips and falls into an alternate universe and thinks “Oops! I’ve always worried about this!”, It better be a comedy.