Life turns on small choices.A last-minute decision to take a shortcut over a snowy pass.A shrugging dismissal of the odd-looking man in the long coat standing off to one side.A decision to postpone a physical exam till a less busy time.A word spoken with the best intentions.Looking back, after the lives are destroyed, the blood spilt, the families shattered, and even the courses of nations changed forever, the mistakes that started the doomsday clock ticking down often seem minor, even innocent-even virtuous. So easy to make.David Eller would give anything-no, everything-to go back and undo those mistakes. But life does not give us that chance. Like everyone else, he has no choice but to dangle from the hand of that clock, trying in vain to pull them backward as they tick inexorably toward zero.