If you draw random samples from a population "enough" times and chart the sampling distribution, it will begin to look like Mr. Gauss' normal distribution (even if the underlying "original" distribution didn't look anything like a bell curve). It's the nature of "randomness" and one of the incredible facts of the universe. PS On a side note: this is what Mr. Gauss looked like on the 10-Deutschmark-bill (note the normal distribution curve in the background)