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> they have to have some clue about the domain, because the domain is their own problem

They can be lifelong experts on their problem, yet have no clue about writing a database engine and low-level programming in general.

> Antirez said literally he didn't know about existing solutions when he went to write redis

Nobody is born with knowledge. The difference is that Antirez studied previous solutions, studied how to do it, and then applied that knowledge right.

Instead, that person did the equivalent of building a bridge disregarding everything humans learnt about it since the Roman empire. It will not be a surprise if the bridge ends up collapsing.