This is why you buy a dozen eggs, why the day is split into two twelve hour segments and why a gross is equal to twelve dozen. When people switched over to the current base 10 system, ten, eleven, and twelve were hold overs because most of the peasantry that could count rarely needed to go higher than twelve.
I know, it's a joke, but behind every joke is some truth. And there are men and women that make a living answering these questions.