We were gliding along Interstate 5 last week, heading down to San Diego for a short vacation. My wife was beside me in the passenger seat, eagerly criticizing my driving while staring at the barren scenery.“Only 320 miles to go,” I chirped. “At 75 miles per hour, how long do you think it will take to get to San Diego?”By the silence that ensued, it was clear that either (1) she didn’t know, or, more likely, (2) she didn’t want to think about it.