They do note that expectations and rapport with the therapist can influence the success of the hypnosis. Milton Erickson emphasized less a biologically determined capacity for hypnosis. He attempted to find metaphors suitable for each individual. He also would use deepening techniques. He felt that individuals who seemed to have a limited capacity for trance could still achieve trance states with proper technique.
Many clinicians approach their hypnotic work from a middle ground.
It is useful to get a sense of the patient's capacity to easily achieve trance. However, much can be done to deepen and enhance the trance state. Additionally, a great deal of productive work can be done while an individual is in a light trance state. The induction is essentially a ritual that helps formalize a transition to a more focused state of consciousness. Deep or light trance states can occur spontaneously.