As I understood it, the original metaphor had you shaving yaks not for the shorn yaks but for the yak hair, which you needed for a thing, which you needed for a

As I understood it, the original metaphor had you shaving yaks not for the shorn yaks but for the yak hair, which you needed for a thing, which you needed for a thing, etc, having passed up alternatives along the way that could have been acceptable but were rejected out of some unspecified combination of perfectionism and Not-Invented-Here.