Quick who said, “It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so?” If any of you confidently declared “Mark Twain” or “Will Rogers,” well it just ain’t so. In fact, it was another American humorist by the name of Josh Billings. Ignorance, it seems, is not merely bliss, but conviction as well. Why is it so hard for us to utter the words, “I don’t know” instead of bluffing our way through it? Our next guest has a theory about that — in fact the theory is named after him. David Dunning is an experimental social psychologist at Cornell University who specializes in the field of confident ignorance.