Can Someone Explain to Me How Things Like This Happen?

A friend and I were out for a late night walk and stumbled (not literally) across this lone tennis shoe laying in the gutter on the side of the street.

Where did it come from?  Where's its mate?  Why didn't its owner notice its absence (almost immediate, I'd imagine) and retrieve it?

I'd be a little more understanding if the pair were laying there, the lone shoe was demolished beyond repair (and therefore unwanted), etc.

Another mystery of the universe, I suppose.