The problem is the lack of a feedback loop. Formal requirements will never accurately reflect what is actually needed unless there is a feedback loop that makes

The problem is the lack of a feedback loop. Formal requirements will never accurately reflect what is actually needed unless there is a feedback loop that makes it possible to improve/update the formal requirements as problems/issues are discovered during development. Changing a single UI element requested by astronauts apparently takes a year for NASA and a day for SpaceX. Guess which software works best?