Open any random data set — populations, river lengths, stock prices, address numbers. Look at the first digit of each. You'd expect 1 through 9 to show up equally. They don't.
Benford's Law
About 30% of numbers start with 1. Only 5% start with 9. The smaller the digit, the more often it leads. It's a rule found in nature, not a theorem someone invented.
Tax fraud investigators use Benford's Law. Faked numbers usually have too-uniform first digits — a giveaway.