The first thing I tell potential clients is that I can't make people fly by flailing their arms no matter how much hypnosis I do. Hypnosis is not magic.
Habits like smoking and overeating are very resistant to change. Hypnosis will not "make" someone lose 84 pounds in six weeks no matter how good my services are. Hypnotherapy cannot be used to force change. It can only motivate a willing client to change.
Once in a while someone will ask me, "Why would anyone come to see you if they didn't want to make that change?" In actuality, sometimes clients come because someone is pressuring them - "If you don't quit (drinking, gambling, etc.), I'm going to leave you." They are not in my office to change. They are there to pacify this other person.
Sometimes parents come in with a teenager saying "make this kid quit running around with the wrong set of friends or drinking or drugging" while the child sits there with her arms crossed and defiance written on her face. There is little likelihood of real change in such a situation.
Medical doctors and psychotherapists send clients to me as an adjunct therapy to their work. If the person is coming only to pacify their doctor or therapist and does not want to deal with their issue, hypnosis will be another failed attempt. Hypnosis is not magic.
But when the client is ready and wants to change, hypnosis can be a valuable tool to make wonderful changes physically, mentally and emotionally.