[nickff]

Are you willing to pay 10x more for the product with that supposed extra reliability (100% vs 99.99966%)? Before you answer, you must remember that perfection cannot be proven ex-ante, it can only be assured.

You should also keep in mind that real systems have fault modes aside from software bugs and hardware glitches, such as unanticipated edge cases and user error, which may dominate your actual failure statistics.