I think what Wacotic said about your type is a good example how your hidden agenda works. It takes you a long time to accept a new idea (like your type) because you're worried that if by any chance you got it wrong and belived in the new thing or idea it would be painful for you to change you're idea. You don't want to totally believe yet that your type is ISTJ because something that you believe in you like to keep as a belief. If your type turned out to be something other than ISTJ you would find it hard to rediscover your type and figure it out again. You'd perfer to get it right, without a doubt, the first time so you don't have to refigure what to believe in.
That sounds just like me. Makes me wonder if I'm really an ISTJ. I thought I was an INFP, but more and more I doubt that I am. Maybe Hugo should include something about hidden agendas in his test.