I have my motto: 'correct the result - privately, praise the person - publicly'.

This does not work many times because the person, whose result needs corrected, makes the result her/his personal characters/properties and gets offended by any attempt to correct the result.

To put that in Buddhist context -- 'anatta' is not appreciated. What more is this: the 'result' becomes a chain on her/his neck and becomes permanent 'dukkha' even when the world has changed. ;-)