It's Time for Pi
Pi is the number you get when you take any circle, measure the distance around it, and divide by the distance across it. Any circle. A dinner plate, the moon, a ring you draw in the sand. Always the same number. About 3.14159, and then it keeps going forever without repeating.
That last part is the part that gets people. It never ends. It never settles into a pattern. You can compute a trillion digits and you are no closer to the “end” than when you started, because there is no end. Pi is irrational (you can’t write it as a fraction) and transcendental (it isn’t the root of any nice polynomial), which are two math-flavored ways of saying it refuses to be pinned down.