One of the most insidious sources of confusion, I find, is the distinction between the meaning of a word and its most frequent uses. It ties into the whole "Applause Lights" phenomenon, particularly "Fake Norms".
P.S. Belatedly: Welcome to Less Wrong! Feel free to introduce yourself in that thread.
This is our monthly thread for collecting these little gems and pearls of wisdom, rationality-related quotes you've seen recently, or had stored in your quotesfile for ages, and which might be handy to link to in one of our discussions.