O'er the land of the free and the home of a pessimist

I just got back from buying an American flag to replace the one I bought last year, which is already faded.

There were three different sized flags to choose from. I'm obviously not good at math, but with only three available you'd think I'd have a pretty good shot at picking the correct size.

Yet somehow, I can't get help thinking that the chance I bought the right size is almost nonexistent.