At some point during your work week, someone is going to ask you for information you don’t have. There are some people (I don’t happen to be one of them) who hate to say “I don’t know.” For some reason, it makes them feel stupid, or out of touch. I never worry about that. I know lots of things, so missing an answer at any given time doesn’t make me feel dumb. In fact, it’s why I almost never use “I don’t know” by itself; I think of it as an incomplete sentence. “I don’t know, but I’ll find out” is my idea of a complete sentence.