One day, while driving through a Wal-Mart parking lot, I saw a small truck slowly rolling backwards—and heading straight for a ravine at the far edge of the lot. I pulled up beside the truck and noticed that it was unoccupied. With some effort I stopped it, but I could not get it to stay until I wedged a small stone behind the rear tire. Looking back, I assume the driver found the truck and I assume he might have said, “Wow, I thought I had it in gear!” Those are famous last words: “I thought.”