Pope Benedict XVI stunned the world earlier this week when he announced his resignation, becoming only the second pope to resign in history, and the first to do so since the Middle Ages. Benedict cited his advanced age and his failing health, noting that the demands of his work were such that he could no longer reliably keep up. His resignation brings to light a truth few in the business world are willing to admit: that in many operations, leaders stay at their posts far longer than they should, and after the point where they are no longer able to perform adequately. We all get old, but the importance of endurance, stamina and the ability to keep one's energy high on a consistent basis is more important than anyone cares to admit.