The real issue in the context of the plate seems to be a general heuristic that people aren't trying to deceive us.

Not surprisingly then, a key element of most magic tricks is misdirection, or outright lying. There was a discussion about this on LW a while back, but I can't find it. Someone mentioned how if you just boldly lie about key elements of the setup, people will form expectations that you can then easily surprise. The commenter then found that this skill at lying (and noticing how trusting people are) bled into the rest of his life, which led me to suggest people should be extra careful around magicians even when they're not on stage!