The underlying theme of commencement, if we are honest about it, is that time passes. Tempus fugit . You walk through a door, and there is no turning back. None of us can stay where we are. Nothing remains the same.
Life is a short run.
You get older. Years slip away. Rogaine or Grecian Formula. And you sit up late nights hoping your kids aren't out doing the kind of things you were doing in high school and college. Human life is fragile and brief.