It's very common, i could remember some dude who was called up by our principal in secondary school days to give a speech on behalf of his hostel but he ended up shaking with the mic in his hand, it was so embarrassing and I could remember some group of girls laughing at his girlfriend, I laughed too but felt pity for the girl cause I would've feel bad if it were my boyfriend.
Not cause he's embarrassing me but what was going through his head and how embarrassed he felt. Some people are like that, they ain't dumb or lack what to say but they're so shy that they can't express themselves in a crowdy or public space without stammering or fidgeting, it's caused by lack of self confidence.
We often see this event happening regularly, whether in schools or churches, mostly found in public gatherings. The cause of it is stage fright or public anxiety.
The audience judges instantly that they have low IQ, are not intelligent, incompetent, or not completely ready for the stage. But deep down, we know that most folks in such a situation are highly intelligent, more competent enough to steal the show. Anxiety should not be used to judge intelligence. In African culture, the conclusion is that the kid is not sharp. If the anxiety is worked on, such a person will be bold enough to address the public in due time.