> I believe dev and QA are separate skillset.

I'm not sure it's a separate skillset. You need the other side's skills all the time in each of those positions.

But it's certainly a separate mindset. People must hold different values in each of them. One just can't competently do both at the same time. And "time" is quantized here in months-long intervals, because it takes many days to internalize a mindset, if one is flexible enough to ever do it.