On the other hand, it is good to search for the affinity between the languages. Python to Ruby can ramp up faster than Python to C#/Java for example. So someone can have a harder time and in the end, won't enjoy the overall framework and leave.
Another example: If you search for someone to take a Next.js project, a React engineer would work well, a Vue engineer might need more time but could also work, but a hardware engineer would struggle and might need too much time to produce.
> Fire fast
2-3 months is way too short for letting someone go, and it is the problem for some startups nowadays.
Most companies onboarding documentation sucks or does not exist, so you can hire a great engineer and think they are not.
There are great unicorn engineers that can manage themselves in the project but most people need some help, feedback, and guidance.
Also, most managers are afraid of giving feedback, I did some consultancies with startups that had managers complaining a lot about a certain engineer, already at the point to fire them. When I asked "do they know that you are unhappy with them?" they always say that they "implied" once or twice. When I give them feedback the improvement is noticeable just in weeks.
Firing fast is sometimes just a cop-out to not give people proper feedback and properly managing them.