The rule that confirms that
as the number of trials increases, the actual probability approaches the expected
probability. If you flip a coin 1000
times, you might get 470 heads. Or 550 -- expected
probabilities of .47 and .55, respectively. But, damn it, the limiting value of that
probability as the number of flips increases without bound is going to be .5.
Brother, if you continue playing that
slot machine, the law of large numbers is going to get your ass.