The art of diagnosis is like a riddle
“I have a riddle,” Paul says, as the dining room falls silent.
“You’re at the bottom of the stairs. And on the wall, there are three light switches labeled one, two, and three. There’s a room upstairs with three lamps, labeled X, Y, and Z.
You can turn on and off as many switches as you want while you’re downstairs, but you can only go upstairs once. And once you’re upstairs, you …