Yeah, I'm probably not the first person to think or post about this, and if I am, then woo hoo!
I wonder if MBTI leads to a self-fulfilling prophecy. You take a test, see what type it gives you, and then you read the description of the type. Because of the label you have been given, would you subconsciously try to act like your label, thus actually "becoming" (or at least acting a lot like) the type despite it possibly being inaccurate? I think this is a real possibility.