As a student, asking questions and feeling safe to say "I don't know" are key to accessing new knowledge or skills. Most adults, however, are uncomfortable admitting they lack understanding because of the fear of being perceived as weak or unintelligent (I believe this is one of the reasons "you can't teach an old dog new tricks" is not as outdated an idiom as we might want to believe). I am no exception-- I hate saying "I don't know" so much, I will say almost anything else to avoid those words coming out of my mouth.
The skill I have struggled the most with over the last ten months of studying is saying "I don't know." Though I've practiced saying it dozens (fine--hundreds) of times, I still cannot utter it without some internal debate first: "Could I fake this one?", "Maybe I can just google it later?", "I have already asked 4 questions in the past ten minutes-- what if I am annoying this person?", etc...
With abundant practice, however, comes sporadic moments of clarity; the proverbial lightbulb that goes on over my head as I realize there was a lesson in that last exchange. I tweeted as many of those lessons as I could recall, as a mini-twitter class I called "#idk101".