Fear is often not rational
Anyone with any phobia knows, rationally, that their fear doesn't make sense. A person with a mouse phobia, for example, knows that mice are not truly dangerous. But they're still scared.
If you're claustrophobic, you know that other people can be perfectly comfortable in spaces that make you panic, but that knowledge makes no difference.
Because rational knowledge exists in a different part of the brain to the part that is creating the anxiety.
And that's where hypnosis comes in.