We joke in class, usually with a smile while rolling our eyes, about having a dumb-dumb-feeling. Its really true, we all get every now and then. It happens in class more frequently than not because we are constantly digging into the unknown, and we are beginners. It sucks, you just get one concept down that took you months to get just to be inundated once again with a new concept to stack on the one you barely just got . I feel at these times a bit lost or overwhelmed in the moment. It usually occurs for me when I am instructed to keep my attention divided on too many things (ie. 13 pts. + absorb-project + condense-expan....you get the point) At first, like in anything, this feeling is met with a sense of doubt that you could comprehend it all. (That's true, but only for now)
It is at these time when I feel like I am making no progress, but I am still training consistently so that can't be the reason. One of my teachers would call these 'plateaus' and that in the internal system of martial arts I must learn to love them. So actually I have come to look for this feeling and not to fret it. My experiences have also shown me that usually shortly after these times I connect some of the pieces and I'm a step further than I was. Baby steps, or stacking sheets of rice paper one at a time or something. So I think of this feeling as a checkpoint in my progress. I figure I will continue to have them the rest of my career so I should get used to them now :).
Another thing is that these dumb-dumb-feelings keep you humble. If I always knew what was going on then my cup would be full...not beginners mind, as we would say in class. This 'full cup' decreases progress. This feeling also ties into the recognizing the ego by 'like, don't like, don't know.' My teacher would say just recognize the feeling, set it aside, and keep training, no way around it.