"Treat production difficulty as orders of magnitude harder than design When asked what problem absorbs most of his engineering time on Starship, Musk's answer was not the design of the Raptor engine but manufacturing it at scale — and he broadened the point explicitly: "prototypes are easy, production is hard" and "it is much harder to take an advanced technology product and bring it into volume manufacturing than it is to design it in the first place, by orders of magnitude." Anyone building a physical product should weight their planning and resources accordingly — the hard part starts the moment the prototype works. Source: Elon Musk, Lex Fridman Podcast, Elon Musk"