He thought he knew that there was no point in heading any further in that direction, and, as Socrates never tired of pointing out, thinking that you know when you don't is the main cause of philosophical paralysis.
-- Daniel Dennett, Darwin's Dangerous Idea
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.
-- Mark Twain
Clearly Dennett has his sources all mixed up.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).