I think that the word "belief" is causing misunderstanding among the group. The term as used in this program is not about beliefs, although these may form part of your "core beliefs and assumptions". It is something deeper than that. I have been trying to find a better term to describe what it means. It is your own personal, unconscious "theory of everything". It comes from all the many patterns you have consciously or unconsciously observed throughout your life. These accumulate to form your view of yourself and the world and you use these to make predictions about what will probably happen next. If you are told you are worthless and can only please by being perfect you may end up believing that you can never do anything right. So part of your core may be that you are a total f-up and your predictions of the outcome of a situation is that you will fail.
To change this core is not easy. You first have to stop believing in the negatives, start feeling, or telling yourself "wrong" every time those thoughts come up. Then you have to work very hard and long again and again to keep doing it or you will slip back into your old "Core beliefs and assumptions" It is so easy to slip back into that familiar core. It happens without even being noticed. So you have to keep vigilant in challenging that negative core.
That's why it is so hard. Maybe it would help if someone outside of you reminded you when you started to slip back. But sometimes they don't see it because we hide it or they become impatient because we keep slipping back into those old patterns.
Does anyone have a better way of explaining it?