Big vessels full of poisonous (but useful!) chemicals. Aircraft control systems. All carefully designed to be far more nines than 99% reliable - provided that the components behave according to their datasheets and how they behaved during validation.
And if it’s critical enough, that isn’t just left to chance after the initial design validation. There are continuous supply chain and acceptance testing checks that have to keep being run and managed. This is one reason the costs are higher.
Big vessels full of poisonous (but useful!) chemicals. Aircraft control systems. All carefully designed to be far more nines than 99% reliable - provided that the components behave according to their datasheets and how they behaved during validation.