From Priceless by American author, columnist and skeptic William Poundstone:

“This says that flipping a fair coin a large number of times will give you a percentage of heads close to 50. That is all you can ask of a fair coin. You can’t predict the outcome of a small number of tosses. However, Tversky and Kahneman noted, people want to believe just that they suppose that’s flipping a coin 10 times will yield five heads and five tales, or something close to it. In reality, lopsided outcomes (like eight heads and two tails) are more common than people believe. Tversky and Kahneman Survey aid some mathematical psychologists at a meeting and found that even the experts were subject to this error. The article’s most memorable line displays a playful with it rarely encountered in scientific papers: ‘peoples intuitions about random sampling appear to satisfy the law of small numbers, which asserts that the law of large numbers applies to small numbers as well.”

Put simply, the more times an experiment is run, the closer the average result will be to the expected value.