A professor holds up a glass of water in class and asks students to guess its weight. After various guesses, he asks what would happen if he held it up for longer periods of time - minutes, hours, days. While the weight wouldn't change, his arm would become sore and possibly need medical attention. He explains that life's problems are like the glass of water - they may seem manageable at first but can overwhelm us if dwelled on for too long. It's important to 'put the glass down' by not stressing over challenges when not actively dealing with them so we can face new problems fresh each day.