This one should help you empathize with other people more.
"Everyone has a secret world inside of them. All the people in the whole world, no matter how dull they seem on the outside, inside them they've got unimaginable, magnificent, wonderful, stupid, amazing worlds."
-Neil Gaiman
I agree with Jiro that the typical mind fallacy is likely a large factor here, but I only see it as affecting the quantity/sophistication of worlds-inside-head, and not the quality that most people have them (I won't go as far as the quote's claim that all people have them, though.). I still agree with the sentiment that it's important to remember that people's inner lives are often much more complex and subjectively rational than we may see from the outside.
Quotes are a unique enough medium of expression that I'm interested in viewing quotes that people have found collectable, emotionally impactful, useful, memorable, or otherwise noteworthy - perhaps others are similarly interested. To clarify, these need not be even remotely related to rationality. I'm hijacking the mandates traditionally used for the Rationality Quotes thread, with a few modifications:
Please post any meta discussion in the top-level comment named "Meta".