They hope that they are not one of the unlucky selected when it comes to tragedy. They believe since these acts are random, no one can plan for them. They feel they should live their life in a way that does not put them in harm's way. Even with the uncertainties and chance of mishap, life is still beautiful. Living life to its fullest is the goal of the optimistic atheist.
Every action has consequences.
Consciousness determines outcome. To a monist, the inexplicable doesn't actually exist. An individual experiencing an event might not fully comprehend the operative factors. However, his faith in the system allows him to metabolize it without conflict. Each of us, if we are to function at a consistently high level, must have a personal belief system.