It works with the vast majority of people but not literally EVERYBODY. There are some people with severe psychological disorders for example, where hypnotherapy is not recommended. In the days before modern Kappasinian hypnotherapy was created (pre-1967) most hypnotherapists just accepted that there were some people who were more able to benefit from it and others who resisted it and were not able to benefit from it. But then Dr. John Kappas created the E&P system for suggestibility and personality/sexual traits. E&P stands for Emotional and Physical. It defines a scale of suggestibility where at one end is an introvert (Emotional) and at the other end is an extrovert(Physical) . Then he created a series of specific questions that determines where on that scale a person is in order to determine the method of learning, and therefore the types of wording that is most effective for their suggestibility type. In this way, we can help most people by tailoring the language in the induction and in the post-hypnotic suggestions to match. The easiest and most ready for this therapy are those that have a 50/50 score on E&P. They are referred to as "Somnambulists". The most difficult are those that score higher than 80% on the Emotional side. Special language is needed in the induction process for them and it takes a little longer.