Before our daughter went off to college, our family took a vacation in Colorado, flying to Denver and renting a car. We visited the Royal Gorge Bridge, which is more than 1000 feet above the Arkansas River. Walking out onto the bridge, I noticed it swayed in the wind. Then a car went past us, and the wood-plank roadway moved beneath my feet. "I don't think I want to drive the car across this bridge," I finally said. "What are you worried about?" our daughter replied. "It's a rental."