Well, thinking about that it's not that hard - you have to trust a lot of people any given day. I've had to trust the elevator guy to have done a good job, the girl at the coffee shop to not poison me. Hm, though I suppose the "not murder me" standard might be holding the bar too low - it's actually interesting to think on the many ways you can die from some nutjob - poisoning your food, push you in the road or on subway tracks, just stab you in a crowded sidewalk, etc.