"I don't know" used to be my default answer in therapy. My T generally doesn't accept it as an answer from me either. In my case, as my T explained, I have spent decades suppressing my own thinking and feelings as a protective measure, that "I don't know" only keeps me stuck in that spot. He challenges me to break down that defense mechanism and say something -- anything -- without sensoring myself (which I began to see the "I don't knows" were all about even though I didn't realize it at first).

Over time, the "I don't knows" grew less frequent as I began to allow myself permission to actually verbalize what I had been suppressing for so long. It took trusting my T and myself enough to risk saying something that I wasn't sure of or wasn't completely comfortable with. Scary step to take, but that is where progress really started.