How exactly would they become "unflushable"?

Also, surely if they were excellent candidates then you'd be doing your absolute best to keep them around?

> Also, surely if they were excellent candidates then you'd be doing your absolute best to keep them around?

Well to be fair excellent candidates are excellent on paper. It sometimes happens (not often, but not once in a blue moon either) that the candidate turns out to be completely unsuitable for the job.