[Banana699]

Eh, I respectfully disagree to your disrespectful disagreement. Things are just different, there is no way around that.

Citing past experience is cheating, if you had already encountered X before to the point that learning it in detail is a negligible cost to you, then you're not truly unfamiliar with X, you amortized (part of) the cost of its learning over the past encounters.

There is no way, and I mean no way, a e.g Java programmer is going to be productive in a Haskell without a 3/6/9-month (depending on how much learning is "productive") learning phase where they are, most of the time, a "read only contributer". Java and Haskell are just too different computing machines entirely. Bad practices here are good practices there, good practices here are bad practices there, how I can describe it? It's literally programming a different abstract machine, they both eventually compile down to electrons but the journeys they take are vastly different.

I think the post title must contain an implied "And be prepared to mentor them while they are being unproductive". In the jumpy 3-years-at-most-per-job world of most tech jobs, that's unacceptable for employers unless they're really desperate.