This is one of the most common misconceptions about hypnosis and it's not too surprising, considering the way hypnosis is presented in movies and on stage.
Maybe you have seen a stage show where one person just didn't respond to a particular skit. In many cases, that is because that skit wasn't "congruent" with who they are. That is, they didn't like the idea, couldn't visualize it, or even found that it conflicted with some value they hold. When you are hypnotized, every word the hypnotist says still gets analyzed. If it sets off any alarm bells, you will either disregard it like that person on stage or even come out of "state" and "awaken".
You might choose to imagine yourself as an ex-smoker, because you don't object to that, but with certainty, you are not going to tell me the P.I.N. for your debit card or do anything you would object to.