Unplanned surprises, or "happy accidents," as Bob Ross would say—those are my favorites.
As I stood facing the exit of this tunnel, I heard the pat- pat- pat- of an approaching runner. With just seconds before he would disappear, I stooped over, placed my camera on the pavement, and—without checking frame or settings—snapped the shutter. This is a(n untouched) favorite of my favorites, and a reminder to go with my instincts.