Now, here's your fallacy.
And, let me also say.. your description of the human thought process is all wrong. :) Consider it this way. When someone walks up to you, and sticks out their hand to shake hands.. you respond by reaching out and shaking hands. You're not processing it all the way you described. You don't think "Oh, this person wants to greet me, I should respond accordingly." That doesn't happen. At all. What actually happens is, their body language communicates to you that they want to shake hands, and the learned response kicks in.. automatically.. and you reach out your hand, before you've thought much of anything. That is why Derren's "interrupt" mechanism works. You watch for a person on the street who is in deep thought, probably remembering something .. memory is an activity that engages the subconscious. Then you interrupt them, and get them to shake hands.. they'll respond, also subconsciously.. and then instead of going with the normal routine of letting go of the hand and letting them run their "normal hand shake routine" you do something different, and you quite literally inject a new thought into their minds. The programming techniques Derren demonstrates, and explains are used widely in sales, in public speaking, and so on. Not everyone is susceptible to them. But many are.