The professor holds up a glass of water to demonstrate to students how problems that seem small can become overwhelming if dwelled upon for too long. While the weight of the glass did not change, the professor's arm would begin to ache after holding it for an hour and could become numb or experience muscle stress if held all day. This represents how small problems may seem manageable at first but can paralyze us if we think about them constantly without respite. The lesson is that while it is important to consider life's challenges, it is even more crucial to "put the glass down" or stop dwelling on problems at the end of each day so that we wake up fresh and able to handle what comes our way.