Benford's Law is my go-to example to show just how bad people are at making up numbers.

The first digit of numbers found in nature - generally measurements, completely irrespective of scale - fit a pattern: a 1 happens 30% of the time, a 2 happens less often, and so on in a logarithmic fashion; a 9 happens only 5% of the time.

Imagine the surface area of a lake in feet. Going from 1000 feet to 2000 feet requires doubling, whereas going from 9000 feet to 10,000 feet is just a small increase of ~11%. Switch to square meters, or square miles, it doesn't matter.