A shoeseller meets a mathematician and complains that he does not know what
size shoes to buy. “No problem,” says the mathematician, “there is a simple
equation for that,” and he shows him the Gaussian normal distribution. The
shoeseller stares some time at het equation and asks, “What is that symbol?”
“That is the Greek letter pi.” “What is pi?” “That is the ratio between the
circumference and the diameter of a circle.” Upon this the shoeseller cries
out: “What does a circle have to do with shoes?!”