I have no idea where you're going with this, but getting the spec right is very different from actually finding a proof for it. I never said actually finding the proof was always easy. But I will say this for sure: getting the spec right and finding a proof for it are jointly much easier than writing a nontrivial bug-free program without a theorem prover. The success or lack of success of waterfall is not relevant here, as that has very little to do with formal verification; additionally, the success of most software methodologies is not measured solely on whether the end product was correct.