Sole survivor

I was driving home from work yesterday and saw a lady's spiked-heel shoe lying in the gutter.  I only saw one, but that doesn't mean its better half wasn't nearby.  Usually though, when I spot a shoe in the street, I only spot one.

Can anyone shed some light on this phenomenon?  I'll bet I spot a shoe in the street once or twice a month.  I don't spot mittens or hats or scarves or anything else that I think would be easier to lose.  I don't spot jackets or purses or billfolds.  I don't spot books or thermoses of coffee.  I spot shoes.  More accurately, shoe.

Who is losing all of these shoes?  How does someone lose a shoe and not go back and get it?  How does someone lose a shoe at all?  I don't believe my shoes have ever fallen off of my feet, especially not a tennis shoe (by and large the greatest majority of my shoe sightings).  I have kicked off my shoes, but not normally in a moving vehicle and definitely not out the window of a moving vehicle.

When I see a shoe in the street, I imagine someone in the vehicle got mad and threw the shoe out of the car window.  I also thought the shoe could have been left on the top of the car and slid off after a while, but who puts shoes on top of the car? 

Anyway, if there is a hidden meaning or signal or even a gang-related reason for shoes to be going solo in the street, I'm too stupid to know it.  Please don't tell me if it will freak me out because sometimes ignorance is indeed bliss, but if there is a simple explanation then let me know.  Thank you.