For hypnosis to work on someone you don't have to believe in hypnosis but you must also be a willing subject for the hypnosis to work.
If you are not willing to be hypnotized then the hypnosis won't work.
For example if you just go up to someone randomly and try to hypnotize that person then it won't work because that person is likely not willing to be hypnotized.
So you must be willing to use the hypnosis and not resist in order for it to be effective otherwise the hypnosis will fail.
That's why stage hypnosis people have people come out of the audience as they are willing to be hypnotized.