Because a circle is the only shape that you can't orient in such a manner to drop into the hole.
Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction. - Ernst F. Schumacher
No matter. Try again. Fail again. Fail better. This time, do it with this tiny ad:
a bit of art, as a gift, that will fit in a stocking