I know there are theorems about floating point, that's missing the point, what I am saying is that the theories most useful for doing reasoning are often nearly

I know there are theorems about floating point, that's missing the point, what I am saying is that the theories most useful for doing reasoning are often nearly impossible to formulate if you would like to include in them a lot of messy details of something like floating point, just as one example. What happens instead, we reason using nice idealized theories, and then we experiment to asses the gap between theory and reality. I am completely a fan of theory and proofs, but the point of the quoted comment is that there is an empirical component to software development too, and your original comment seemed to question it.