A professor holds up a glass of water in class and asks students how much they think it weighs. When students provide guesses, the professor notes he doesn't actually know unless he weighs it. He asks what would happen if he held it up for minutes, then an hour, then a day. While the weight wouldn't change, holding it for longer periods would cause muscle strain and pain in his arm. He tells students it's important to think about life's problems but more important to "put the glass down" at the end of each day to avoid stress and feel refreshed. We should remember to let go of problems when we leave work each day.