The professor holds up a glass of water in class and asks students to guess its weight, which they do. He then asks what would happen if he held it up for longer periods of time - minutes, hours, days. While the weight would not change, his arm would become sore and possibly numb. He explains that life's problems are like the glass of water - they seem manageable at first but can overwhelm us if dwelled upon. The key is to "put the glass down" at the end of each day to avoid stress and start fresh the next day able to handle what comes.