Why do you run so much?

Here is a question I am asked nearly as often as I check my mail: why do you run so much? Well I could blow your mind with some wonderfully colorful, and conscious expanding running epiphany . . .

but nobody’s got time for that.

I run to challenge myself.

I run to  strengthen myself.

I run to free myself.

I run because I can.

What drives you to run?