This. The right way to think is that each component, in parallel, have a chance of succeeding, so chance of total system failure is exponentially small in the n

This. The right way to think is that each component, in parallel, have a chance of succeeding, so chance of total system failure is exponentially small in the number of components. Not: oh if this layer fails, the next one will catch it... which makes the chance of failure as high as the weakest link.