This past week I've been converting my upstairs office into a nursery. That means hauling every piece of furniture downstairs to the basement, then turning around and hauling a different set of boxes and furniture back up. At one point I was carrying two boxes stacked on top of each other, a bag looped over my wrist, and my car keys pinched between two fingers — convinced I could squeeze in one more trip. My wife offered to take one. I said, "I've got it." Three steps later,