Fun Facts and 'Rules of Thumb' Collection

I enjoy trivia, fun facts, and rules of thumb, like:

When you're playing blackjack, assume that any unseen card is an 8.

Party planning: one toilet per keg of beer

If you are assaulted, scream Fire! People are more likely to come to your aid than if you shout Help!

THE SURVIVAL RULE OF THREE: You can live three seconds without blood, three minutes without air, three days without water, and three weeks without food.

Please share yours or any good ones you find.