More diplomatically: people are terrified of disapproval and will do anything to avoid feeling they deserve it, so if you must point out that something isn’t working, try to do so in such a way that the easiest way for them to resolve their cognitive dissonance isn’t “blow you off” or “get mad at you”. i.e., find a way for them to “save face”.
(As a lot of people associate being incorrect with being deserving of disapproval.)
More diplomatically: people are terrified of disapproval and will do anything to avoid feeling they deserve it, so if you must point out that something isn’t working, try to do so in such a way that the easiest way for them to resolve their cognitive dissonance isn’t “blow you off” or “get mad at you”. i.e., find a way for them to “save face”.
(As a lot of people associate being incorrect with being deserving of disapproval.)