Be firm about the standard and warm about the person. Most people only manage one.

Those two things feel like opposites and they are not. Most people pick a side: either they go soft on the standard so nobody feels bad, or they hold the line and treat the person like a problem. Both are the easy version. Keeping the bar exactly where it was while making it obvious you are on someone’s side takes more effort, and it is the only combination people actually trust.

Next time you have to tell someone their part is not good enough, say both halves in the same breath. Name the gap plainly, then say you think they can close it and offer one specific hand.