Why do some numbers show up more in real life?

Open a book of facts about rivers and mountains and countries, and something weird happens. The first digit of each number — the leftmost one — isn't random at all. About 30% of the time, it's a 1. Only 5% of the time, it's a 9. If numbers were fair, each digit would show up about 11% of the time. But real-world numbers play favorites.
This pattern is called Benford's Law, after a physicist who noticed his logarithm tables were more worn out at the beginning than the end. People looked up small leading digits way more often. It turns out this isn't a coincidence — it's how numbers that grow and shrink in the real world actually behave.
