And think about how many layers of safety margins. If there are ten subsystems each with a 20% safety margin to say that their designers did their jobs right,

And think about how many layers of safety margins. If there are ten subsystems each with a 20% safety margin to say that their designers did their jobs right, then you might have an overall system with as much as 200% safety margin. (yeah not everything is linear like that, but illustrating the point.)