A professor walked in on the last day of class before graduation to teach a final lesson. He asked, "How heavy is this glass of water I am holding?"  The class shouted out answers ranging from ounces to pounds. Then the professor said, "From my perspective it is all about how long I hold it.  Hold it for a few seconds, and it is easy, hold for an hour and it is quite heavy, hold it all day and my arm cramps and becomes paralyzed and I drop it."
Now he had the classes' attention.  The professor f...