“Your strength as a rationalist is your ability to be more confused by fiction than by reality. If you are equally good at explaining any outcome, you have zero knowledge.”

“Doing worse with more knowledge means you are doing something very wrong.”

“A true rationalist ought to be effective in the real world.”

“One of chief pieces of advice I give to aspiring rationalists is "Don't try to be clever." And, "Listen to those quiet, nagging doubts." If you don't know, you don't know what you don't know, you don't know how much you don't know, and you don't know how much you needed to know.”

“Lies propagate, that's what I'm saying. You've got to tell more lies to cover them up, lie about every fact that's connected to the first lie. And if you kept on lying, and you kept on trying to cover it up, sooner or later you'd even have to start lying about the general laws of thought. Like, someone is selling you some kind of alternative medicine that doesn't work, and any double-blind experimental study will confirm that it doesn't work. So if someone wants to go on defending the lie, they've got to get you to disbelieve in the experimental method. Like, the experimental method is just for merely scientific kinds of medicine, not amazing alternative medicine like theirs. Or a good and virtuous person should believe as strongly as they can, no matter what the evidence says. Or truth doesn't exist and there's no such thing as objective reality. A lot of common wisdom like that isn't just mistaken, it's anti-epistemology, it's systematically wrong. Every rule of rationality that tells you how to find the truth, there's someone out there who needs you to believe the opposite. If you once tell a lie, the truth is ever after your enemy; and there's a lot of people out there telling lies.”

“‎If you regard evidence as a constraint and seek to free yourself, you sell yourself into the chains of your whims. For you cannot make a true map of a city by sitting in your bedroom with your eyes shut and drawing lines upon paper according to impulse.”

“No..." said Professor Quirrell. "That is not why I am here. You have made no effort to hide your dislike for me, Miss Granger. I thank you for that lack of pretense, for I much prefer true hate to false love.”