One million people enter a coin-flipping contest. The winner becomes a Supreme Court Justice. Everyone flips at once, and you live to flip again if your coin lands on heads. Statistically, it will take about 20 flips to crown our champion. That is because the odds of flipping a coin 20 times and landing on heads each time is one in a million.

Of course, lower probability outcomes would be possible. So 20 flips is just a statistical average, not the number that it will take every time. Because we are using the contest (and its math) as a metaphor, let’s just go with 20 flips.