> You could also have a counter of problematic area's: some parts are easier to break than others, and could be improved/made more robust...

Oh yes. Nothing I said should be read as precluding that. High-risk components cause more fallout when they break, that's how it works. Or fragile components break easily. Sure.

But it's wise to keep an eye out for people who are seriously problematic and to establish a pattern of problem-causing, for the purposes of remanding to HR.