Question for the Ages

What is with those single shoes you see on the side of the road? It's a constant thing, glimpsing a solitary shoe lying, alone and stoic, on the shoulder.

How do they get there? Does someone pitch a single shoe out of a car window as he or she speeds past? And if so, why? Is it the shoe of someone they've a beef with who is sleeping soundly in the back seat, oblivious to the impending shoelessness? Is it just an extra shoe that they found stuffed into the glove compartment?

Did someone walking by experience sudden, unexplainable massive foot growth that forced them to immediately pull off the offending article and throw it down upon the gravel-strewn earth?

Is a higher being leaving shoes around in various locations on the earth, linked together in some sort of code to produce a message about the meaning of life and our place in the world?

Where do the fucking shoes come from? And why is there always only one?