There is a classic Dave Chapelle bit where his friend gets pulled over for driving recklessly. After being confronted he says to the cop, "I'm sorry officer, I didn't know I couldn't do that." The officer, to Dave's shock, replies, "Well now you know! Get outta here!". Then Dave's friend turns to him and says, "That was good, wasn't it? Because I did know I couldn't do that!"

This is how QI works.