I remember some years ago taking one of my first walks in San Francisco with my then three-year-old twins. I looked at the map, and it didn't seem like such a big deal to go from one place to the other. After all, it looked flat on the map! But as my wife and I began the trek we quickly realized that this was going to be no easy stroll. Shouldering backpacks filled with three-year-old paraphernalia and dragging tired twins behind, we climbed high and hiked low. We were quickly exhausted. We stood on the corner, with children crying and the two of us questioning our sanity, wondering what we would do next when a taxicab pulled up right beside us.

I leaned into the window as the driver stretched across the passenger seat. We met eye-to-eye, nose to nose. "Where are you going?" he said. We di…