I'm currently reading Mailer's 'A fire on the moon' and have reached the part where he describes, in detail, the number of spare circuits, pipes, valves and so on that formed a part of each Apollo rocket assembly.
I got to wondering: If they could have been absolutely certain that nothing would go wrong, and that every part would work flawlessly and no accidents or emergencies would happen, how much smaller could the rocket have been? How much mass did all the extra safety mechanisms amount to in the system?
Apollo 13, obviously...