I dropped my oldest son off at the airport this afternoon; he's heading to Las Vegas for week-long Microsoft conference. I'm back home but following his flight on FlightAware. Why do I do that? For the same reason you watch your loved ones go through security, just to make sure they get through OK, and you don't turn to head back to the car until you can't see them anymore.
As I watched today, a man about my age and his wife took up their post near me.
"You just want to hold on to every last moment," he said to me.
"Yeah," I said, as I turned and headed for the garage. "I know."