The limits of knowledge
A great anecdote from Daniel Ellsberg about what he told first-time government employee Henry Kissinger about the power and limitations of the security clearances he was about to receive.
First, you'll be exhilarated by some of this new information, and by having it all -- so much! incredible! -- suddenly available to you. But second, almost as fast, you will feel like a fool for having studied, written, talked about these subjects, criticized and analyzed decisions made by presidents for years without having known of the existence of all this information, which presidents and others had and you didn't, and which must have influenced their decisions in ways you couldn't even guess. In particular, you'll feel foolish for having literally rubbed shoulders for over a decade with some officials and consultants who did have access to all this information you didn't know about and didn't know they had, and you'll be stunned that they kept that secret from you so well.
(thx, micah)