There is no concept of "evil" or "crazy" in objective reality, but there is a concept of "people". The quote reminds us that understanding human behaviour begins by accepting that people do what they do exactly because they are people -- that is, instances of a very specific mental architecture forged by blind evolution in very specific circumstances on this specific planet.
(Last month's started a little late, I thought I'd bring it back to its original schedule.)
A monthly thread for posting any interesting rationality-related quotes you've seen recently on the Internet, or had stored in your quotesfile for ages.