When my friends and I had learned about the Doppler effect, we were all at Level 1, maybe with minor inroads into Level 2. The problem? I classified that as "not understanding", while my friends called it "complete understanding".

I had a friend express frustration with me once, because we would have conversations about some subjects she felt she understood, in which I would say things like "I don't understand X", and then proceed to demonstrate what she felt was a better understanding than she had. I think it felt to her like I was "sandbagging" when claiming I didn't understand things, whereas I was merely expressing that I was somewhere between levels 1 and 2 and was unsatisfied with it.