I had never imagined myself a Swiss-cheese learner

until the day I started to take learning English seriously.

When my son was in grade school, the one thing he did that upset me the most was that he took concepts that he didn't 100% understood as something he knew. And whenever that happened, I showed him my own example: look at mom, she always knows what she knows, how much she knows, and what she doesn't know. (And it is fine that you don't know something, no matter how essential it is!)  Ironically I am now facing the same situation myself. The only difference is that with my son, it happened occasionally, with me, it appears consistently. I just have so much fuzzy knowledge in the English language to be cleared up.