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 lead to muscle stress if held all day. This represents how small problems may initially seem manageable but can paralyze us if we focus on them constantly. The lesson is that while problems should be thought through, it is important to "put the glass down" or stop thinking about problems at the end of the day so we can wake up fresh and able to handle challenges in a healthy way.