Quoting Will Lockett

Musk isn’t an engineer and doesn’t understand iterative design, and now SpaceX and NASA are facing a sunk cost fallacy.

You never achieve iterative design with a full-scale prototype. It is incredibly wasteful and can lead you down several problematic and dead-end solutions. I used to engineer high-speed boats — another weight- and safety-sensitive engineering field. We would always conduct scale model tests of every aspect of design, iteratively changing it as we went so that when we did build the full-scale version, we were solving the problems of scale, not design and scale simultaneously.