I don't know

Is it only me or is it everyone who finds that "I don't know" is the toughest thing to say? Oh, I mean, yes, if someone asked you to explain the different String theories, 'I don't know' comes tripping off your tongue like greased lightning. Probably laced with that 'What sort of idiot expects people to know such things?' tone. Unless, of course, you are a theoretical physicist.No, I do not mean