"Prototypes are easy, Manufacturing is hard!" is a statement made famous by Elon Musk who did not see it as a statement to be accepted. Instead Tesla turned the challenge inside out, and focuses on vertical integration, and on designing their products in such a way that they among other things are built to comply to another of Elon's mantras: "A good part is NO part".
And the discipline goes deep: Unlike other car companies Tesla is highly vertically integrated, and they make many of their own parts themselves. When they do involve external suppliers, they deploy their own employees to help set up the production lines of the supplier, and remain involved with the changes in the design as manufacturing takes place and Tesla's demand requires changes to the parts coming in on the next delivery. This happens not just for first tier, second tier or third tier, but all the way to the mining of the raw materials.
This allows Tesla to have better insight into their business, and provides great input for their own software on the manufacturing process.