Okay, I feel silly. I get beyond the first exercise in session 9; going beyond and thinking more about my answers. I look back through program and realize that I've not challenged core beliefs, but negative thoughts. I understand now. I also agree with second exercise which is somewhat my question - challenging core beliefs can be a lifetime thing. Which is good, it means I don't get to keep them all pent up inside once I get some of them out, I just keeping on identifying them.