Funny. You keep telling people that what they can't do, despite people telling you that they do indeed find their PCs taking unexpected turns.This is the same kind of argument used when it's claimed that authors feel the characters are writing themselves -- it's not really true. You're authoring the character. At no point is anything about the character at stake. It's a safe space to imagine within.
And, again, this is fine and good and I enjoy doing this. I don't try to dress it up flowery-like, though, to try and claim my safe acts of authoring are exploration of the character. Everything that's happening is me making choices about how to express the character -- nothing is discovered about the character through play.
I'm not trying to bag on you, here, but to point out a pretty salient difference in how roleplaying can be approached. I tend to see that the strong aversion to staking character is closely tied to primary experience or preference for games where the GM has all or almost all other authorities in the game -- like D&D. Here it's the only holdout where the player has full authority to declare character while the GM presents the world. Even here, there's close correlation to play in the Trad or Neo-Trad styles. And, again, nothing at all wrong with that. I'm quite enjoying the Trad Rime of the Frostmaiden game I'm in right now, but I make no qualms that I'm exploring my character even when I put on the funny voice and playact in character -- nothing about my characterization is ever at stake due to the game. Any changes I make are because I want to.
I'm not claiming people are channeling someone, but the decisions people make aren't always conscious ones. It may never be true for you, but it's part of the creative process for a lot of people.
Believe it or not, people aren't all like you. When I get into role playing, DMing or writing stories, there's times when it just flows out without conscious forethought. It doesn't really matter how you label it, but your "it's all you" only tells part of the story.