"Almost immediately when you started work" is precisely too late, though. If you hire purely off GitHub and get someone who lifted their code (instead of forking it), that's a huge price.

Bad hires inflict huge costs up front, in wasted interview opportunities and startup costs and lost training time and morale hits and a dozen other things. "Fire fast" is popular advice because it's better than firing slow, not because unsuccessful hires are a sustainable event.