> How about they just sell coffee and shut up? <
Most people start out reasonable, and somewhat humble. But then success goes to their heads, and they feel the need to preach to the rest of us. We see this with movie stars, athletes, business owners, etc. They know nothing. But they think they know everything.
It would actually be amusing, except that some people actually listen to them.
They know nothing. But they think they know everything.
.............................................
Pretty well defines the Dunning-Kruger effect.
The Dunning-Kruger effect is a type of cognitive bias in which people believe that they are smarter and more capable than they really are.