Maybe it's a big company thing, but every time I've had to end someone's job it took several months of performance management and about 50 to 100 pages of documentation. Imagine about a year of having your team limping and not being able to achieve its commitments, while you have to be polite and supportive to a hostile person who's obviously on their way out but can't see it, and all the while your 1:1 meetings with your boss start with "Sooooo... What's going on with Charlie? Are you documenting? I don't feel like you're documenting." Every meeting you walk into where they ask why "X" isn't done yet, you can't tell them that Charlie fundamentally can't deliver it, because any mention of that is wandering into HR territory, and you can't take Charlie off of "X" because that's going to screw up the continuity of your documentation. Meanwhile, Charlie is wandering around the halls trying to foment some kind of misguided rebellion against you, and (edit: possibly) stealing stuff.
So not really a whim.