This is why Erlang's OTP focuses on supervisor trees. At each level of the component hierarchy, you have redundancy. Subcomponents themselves may have interactive complexity, but a failure or misspecification in any of the interactions making up that subcomponent simply makes that subcomponent fail. This failure is handled at a higher level by doing something simpler.

And "do something simpler" is actually a core part of this strategy. You're right that "today's systems are so complicated that many failures stem from insufficient, misunderstood, or ambiguous specifications". In most cases, yesterday's system worked just fine, you just can't sell it as a competitive advantage. So build simple, well-understood subsystems as fallbacks to the complex bleeding-edge systems, or even just take the software that's been working for a decade.