A few weeks ago Secretary of Defense Robert Gates spoke at my university and ended his speech with a favorite quote from former President John Adams, who in a letter to his son says:
"Public business, my son, must always be done by somebody. It will be done by somebody or another. If wise men decline it, others will not; if honest men refuse it, others will not."
Gates went on to ask:
"Will the wise and honest here at Duke come help us do the public business of America? Because, if America’s best and brightest young people will not step forward, who then can we count on to protect and sustain the greatness of this country in the 21st century?"
You can find the full text of his speech here.