Choose any naturally occurring set of numbers, such as country populations, river lengths, or company revenues, and count only the "first digit." You might expect digits 1–9 to appear evenly, but in reality, numbers beginning with 1 appear far more often — this is Benford's Law.
Why does this happen? As numbers increase, when you move from 100 → 200 → 300 → ... → 900, the range beginning with 1 (100–199) is wider than any other range, rather than simply doubling from 100 to 200. The effect becomes clearer when the data are spread across several digit lengths. (By contrast, numbers chosen uniformly at random do not follow this law — compare them below.)