To be conscious that you are ignorant is a great step to knowledge.

You cannot learn something you believe you already know. Noticing the gap is the part that costs, since it means giving up a comfortable position and admitting it in front of people who may have assumed otherwise. After that the learning is relatively straightforward. Most of what stops people is not difficulty but the reluctance to be a beginner in public.

Pick the subject where you have been nodding along without understanding. Say out loud to someone that you do not follow it, and ask them to start from the beginning.