When Pope Benedict XVI announced that he would abdicate the
papacy, he explained that "in today's world, subject to so many
rapid changes...both strength of mind and body are necessary,
strength which in the last few months, has deteriorated in me to
the extent that I have had to recognize my incapacity to
adequately fulfill the ministry entrusted to me." By becoming
the first pope to resign since the 15th century, Benedict
demonstrated a self-knowledge that is incredibly rare among
leaders. Contrast his behavior, for example, with that of New
Jersey Senator Frank Lautenberg, who before being forced to
stand aside described Newark Mayor Cory Booker as a
"disrespectful" child for challenging his reelection bid, even
though Lautenberg would have been almost 92 when he was sworn
in.  It may be a fraught subject, but aging often has enormous
effects on people's personalities and cognitive function. Some
leaders can maintain their vitality and abilities into extreme
old age, but after enough time in office, a lead