The technical definition for hypnosis is “the bypassing of the critical factor of the conscious mind and the establishment of acceptable selective thinking”.
What this means is that two things need to happen at the same time for hypnosis to occur in a person’s consciousness:
First, the analytical part of the mind that normally rejects new information is bypassed.
Secondly, information that’s acceptable to the person in hypnosis is accepted into the subconscious mind, replacing the old information. Once the old information is replaced it can no longer be acted on. This is very similar to resetting the date and time on your mobile phone. The mobile phone will only use the new information once it's been accepted and this principle is equally true with your mind.
It’s important to note that only information that’s reasonable and pleasing will be accepted by the subconscious mind. The subconscious minds primary task is to keep you safe. To do this it stores all the information you've accumulated in your life and uses this as a reference. The subconscious mind does not need to “think”. It already knows what’s good for you, and what isn't, based on your past experience. For this reason you can’t get people to do what they don’t want to do in hypnosis.
Even stage hypnotists can’t get people to do what they don’t want to do. Stage hypnotists have to use volunteers on stage to present a successful show. All the people on stage during a stage hypnosis show will only do what they consider to be reasonable and pleasing. The stage hypnotist has to fill his stage with people that consider it reasonable and pleasing to play the fool on stage to entertain the audience, or the show will fail. For this reason volunteers are taken from the audience.