Dunning-Kruger effect... There's the 'teacher' side too.
Years later, it dawns on me. It's the same thing.
Someone asks for my opinion on something I know about. So I tell them. Probably too much information for them though. And then... I present the other side, some unknowns, etc. I'm honest -- I'll say I don't know about a certain area. But the bottom line is there's one result (or a range). "This is what you could do, what direction you could go in, etc." But it's their choice.
ie I'm presenting something I know, aware of my limits, and it comes off as not knowing it that well.
Contrast that with Joe-Know-Nothing who confidently tells them to do the wrong thing.
What do they do? Go with the Know-Nothing because his idea is simple and he's confident, although wrong, or they wait and think, but give Know-Nothing a lot of weight in their decision making processing.