Ever needed tomato sauce for your chips, and then tried to grab the attention of the waitron walking past?
It’s more than likely that you didn’t succeed, as your “ahem... excuse me!” didn’t register with said waitron, who subsequently disappeared off to the kitchen leaving you with a plateful of dry chips. If, however, you knew his or her name, it would have been a cinch. “Excuse me John.” “Um, yes ma’am?” “Would you be so kind as to bring me some tomato sauce for my chips please?”
“Certainly, ma’am. No problem.”