The whole reason inception was difficult/impossible is that the subject had to think it was his own idea, and that he'd come up with it completely on his own, with no outside influences. The problem is that if someone tells you or shows you an idea, you forever know that it's theirs. Or something like that. I forget the exact rationale, but it was along those lines.

So. Given that we've just watched a movie about questioning reality, I don't think we can convince ourselves that questioning reality is our own original thought.