I disagree that any car mechanic working a local auto body shop knows engines well enough to design one. They just know which parts are broken.
Similarly we reach a point in coding where you don't really need to know how every API or language you use operates beneath the hood, you just need to be able to see where its broken.
Similarly we reach a point in coding where you don't really need to know how every API or language you use operates beneath the hood, you just need to be able to see where its broken.