This is especially true and contradicts the generally accepted opinion repeatedly expressed around here, that knowing about programming in general is enough to be an expert in any technology in a short amount of time. The reasoning then goes that when hiring, one shouldn't rule out seasoned developers that have no experience in the technologies in actual use. This is an arrogant recipe for pain for the whole team. The myriad combination of interfaces between tools/stacks/technologies cannot be understood expertly in any small amount of time.

I suffered at a polyglot consultancy that shifted people around rapidly between stacks and technologies due to overconfidence in this belief; it is very painful for any programmer with a sense of craft and client stewardship. Of course, if all you care about is banging out a piece of garbage that will hold up until the checks clear, then I guess this doesn't matter.