First of all, nobody "sucks beyond repair" -- everyone can grow and evolve although some people may start at a point where the company doesn't have adequate enough resources to make an ROI off of its investment.

The problem is, some people have a fixed mindset rather than a growth mindset because they've never seen anything different so they think it's impossible. When you say "Sometimes the person sucks beyond repair and needs to be fired" it ends up functioning as a red herring to deflect away from poor people leadership. It's a naive excuse made to hide a lack of understanding regarding how something really works.

To figure that out, let's ask this: how do you think the manager hired that "wrong" person in the first place, and how do you think that person ended up in a place to end up failing?

My point is not to be socratically pedantic here, but to point out that communication is /hard/ and often times an inadequate deployment of it is at the root cause of these kinds of failures. What kinds of communications could have gone wrong here?

1) Failure to adequately communicate with higher ups about headcount, business goals and necessity/capability to deploy extra headcount

2) Failure to adequately communicate requirements for the job before hiring

3) Failure to adequately communicate during the interview so as to properly assess candidates

4) Failure to adequately communicate expectations, progress, onboarding and plans after a candidate onboards

Guess what happens if anything about this chain of processes is broken internally? The candidate will fail, and due to circumstances out of their control. And then they will move to a more functional organization, and wonder why they ever wasted their time with this one.

Now, whose responsibility is it to make the right judgment call about that? Whose responsibility is it to have the right internal /communications/ to make sure the decision is well thought out and solid, to make sure it is brought through to fruition successfully? Who reaps the ultimate rewards, and who ultimately shoulders the greatest burden for mis-execution?

Not the IC. It is leadership. This isn't rocket science.