It's not even a just buzz-mantra, it can come from personal experience. You clean up the crap of a team or a specific few bad apples and you can't get them fired because they deliver fast rushed spaghetti code. And they keep on doing it despite repeated requests for them to stop. You can cut it at the source if you have a chance at the interview step although, because your thumbs down will actually mean something at that step.
But even that can't be the greatest way to screen these people, you often have to work with them for a few weeks or months to see their good and bad sides. Once they are established in the company it can be definitely be harder to get them removed.
> you can't get them fired because they deliver fast rushed spaghetti code
That is a management problem, not a hiring problem.
A couple weeks ago I asked for specific examples in a similar discussion[1]. Most of the responses I got were partially or totally management problems that companies were trying to fix by modifying the hiring process. If your management processes are shit, then you do need to be extremely careful about who you hire, because one bad one can ruin your company. The root cause, though, is management, and the proper solution is to fix your management processes, not hire unicorns.
This is funny because if you had watched the "How to start a startup" class you would have seen that almost no time was dedicated to management practices. Across the board on HN and in other hacker spaces, "Management" is universally derided as something worth studying. In practice it is hugely important and impactful but the tech community doesn't seem to care.
But even that can't be the greatest way to screen these people, you often have to work with them for a few weeks or months to see their good and bad sides. Once they are established in the company it can be definitely be harder to get them removed.