Mental Bungee-jumping may not be your sport of choice, but there's a cerebral ledge that sooner or later each of us has to leap off. One day, ready or not, we glance in a mirror, cuddle an infant, attend a funeral, walk in the woods, partake of a substance Nancy Reagan warned us to eschew, chance a liaison, wake in the night with a napalm lobster in our chest, read a message from the pope or the Dalai Lama, get lost in Verdi or lost in the stars - and wind up thinking about our soul.