When I'm trying to make sure I'm not forgetting something important (other than a child), I check for three things: my wallet, my keys and my phone. I do this because these things tend to migrate away from my purse and getting them back into the purse is Really Important if I'm about to get into a car. Of the three, the least crucial is the phone (everyone else is carrying one, so should I need a phone in an emergency, I could just ask someone else to make a call, right?), and sure enough, I do in fact drive away with the wallet and keys. Occasionally, I'll forget the wallet, but that is very rare.
"We seem never to forget our mobile phones; yet, we sometimes forget our car keys and our wallets."
What kind of person never forgets his phone? It's a serious question.