Hypnosis and being hypnotized is a skill just like catching a ball, crotcheting, or Soduko. As we practice allowing ourselves to access our subconscious mind we get better at it. It becomes easier and more natural to drift into a suggestable state where the real work or reprogramming ourselves can take place.
The first time I tried to swim was terrible. I didn't even know what muscles to flex! I was so uncoordinated I just kind of splashed around and sank. It was a terrifying experience. Eventually, with guidance and practice, I figured out what needed to happen to stay afloat and even how to move forward. Now I feel completely at home in the water. I'm comfortable and confident when I swim.
Likewise, when we allow ourselves to open up or relax we find it becomes easier and easier to reach that wonderful, powerful state where the resources of our own mind can be guided to help us heal. We practice being hypnotized and get better at accessing our subconsious.