A few days ago I asked why people always claim to see the Virgin Mary in random shapes, because it's such an easy shape to get naturally.
But a good scientist always looks to the contrapositive: what about other familiar shapes that are not easy to make? How common are they?
I'd say pretty good. It's what our brains do. We should use those very same brains to understand that the brain tricks us sometimes.
Tip o' the naan to BABloggee Lunar Mark.