He was a beginner. He screwed up a hand about as badly as you can screw up a hand. All he had to do was ruff a few losers in the dummy. Failing that, all he had to do was choose one of his winning finesses.

When the hand was over, he said he was sorry. But it wasn't exactly clear that he knew what mistakes he had made. So his partner explained them to him.

Wrong. Bob sez:

When partner has admitted making a mistake, the discussion is over.

I call this sanctuary. Admitting a mistake gives people sanctuary against criticism.

First, admitting a mistake is not easy. Second, if someone knows they made a mistake, they do not need your criticism. If anything, they need your support. Third, someone else analyzing their own play and coming to their own conclusions is a lot more effective than you analyzing their play and telling them your conclusions.

Someone might admit error just to avoid criticism? Like a thief hiding in a church? That is not the end of the world. If your partner doesn't want criticism, then do not criticize.