Flight software is the most paranoid code ever written, and that paranoia is the product, not a side effect.
The core idea is redundancy with disagreement handling. Multiple computers run the same computation, compare results, and vote. A sensor that drifts is outvoted rather than obeyed. There is no retry-and-hope, because there is no second launch.
Everything is bounded: no dynamic memory allocation after initialisation, no unbounded loops, no surprises in worst-case execution time. Compared to web development, it is an entirely different relationship with uncertainty.
My worst deploy took down a staging environment for eleven minutes. I think about that ratio often.