If you’re a manager, here is a question for you: Is there someone on your team that you would not hire again if you were hiring all over again? If yes, what’s that person still doing on your team? Effectively, not firing them is hiring them every, single, day!
It might be that you don’t need to fire them, but maybe you need to move them into a new position where they realize their full potential and flourish. It’s worth asking this: is this person on the right bus? and if yes, are they in the right seat?