'Smartest' in the room

I've heard from somewhere I cannot recall, the saying, "If you're the smartest person in the room, you're in the wrong room". I'm not even going to ask how they can go about and quantify 'smartness' to compare people in the first place. So let's say you have a way of immediately being able to tell your current ranking in a room full of people. If everyone follows this advice no two people will be in the same room!