The Dunning-Kruger effect suggests that incompetent people over estimate their ability. They are confident when they shouldn’t be. They think they are experts when they clearly are not.
This can happen to speakers who are topic experts but are poor speakers. They know they are topic experts and assume that they are also very skilled speakers and presenters. They falsely believe that because they are knowledgeable they are also able to communicate this knowledge skilfully. They lack the insight to see that content doesn’t sell itself. How information is presented is equally important as the information itself.
The only way out of this delusion is to get honest feedback