Why Some People Can’t Be Hypnotized?

Recently I was asked about why some people can’t be hypnotized. The question came after a man attended a hypnosis stage show and saw that the hypnotist  was able to hypnotize most people, but there were some in the crowd that he couldn’t. 
Here’s my explanation of why some people can’t be hypnotized…
It’s quite simple. All hypnosis is essentially self-hypnosis. The subject is always the one in control. The hypnotist is truly there to give the suggestions that the subject then is more apt to integrate when in a relaxed state. However, if a person says they cannot be hypnotized or are not hypnotizable, they just hypnotized themselves to not take on suggestions from anyone else who would be hypnotizing them per say. Therefore, hypnosis typically won’t be effective for them. 
It should be noted that people who are under the influence of drugs or alcohol are not hypnotizable due to the impairment of their brains. Also, people who suffer from mental illnesses are typically not easily hypnotized.
Therefore the only sober and mentally stable people who cannot be hypnotized are those who say they can’t be hypnotized.
A good stage hypnotist does some suggestibility tests to see how hypnotizable subjects are and then asks those who are resistant to leave the stage. 
In my private hypnosis practice, I find that people have some fear of losing control and often need a couple of sessions to realize they are actually the one in control. Plus, by working with a hypnotherapist they are learning a valuable skill of self-hypnosis.