Another month has passed and here is a new rationality quotes thread. The usual rules are:

• Please post all quotes separately, so that they can be upvoted or downvoted separately. (If they are strongly related, reply to your own comments. If strongly ordered, then go ahead and post them together.)
• Do not quote yourself.
• Do not quote from Less Wrong itself, Overcoming Bias, or HPMoR.
• No more than 5 quotes per person per monthly thread, please.