Far from being pessimistic or nihilistic, as modern uses of the term "cynic" suggest, the ancient Cynics were astonishingly optimistic regarding human nature. They believed that if one simplified one's life--giving up all unnecessary possessions, desires, and ideas--and lived in the moment as much as possible, one could regain one's natural goodness and happiness. It was a life exemplified most famously by the eccentric Diogenes, nicknamed "the Dog,"...