Just about everyone can be hypnotised to some extent, with one specific exception. Yet, while almost everyone can be hypnotised not everyone will be. Sometimes hypnosis is not as good a fit for a person as another delivery system. Hypnosis is a skill, so you improve your hypnotisability each time you successfully enter it.
The exception from the rule is people whose conscious mental functioning is like a very small child. Since very small children have only slightly developed self-conciousness the sense of a change of state that happens in hypnosis would not occur and so the movement from normal waking consciousness to hypnosis and its accompanying sense of absorption doesn't happen.
