Why are stupid people so confident?

because stupid. simple as that.

that's a billion dollar question...

It's because they found there self worth at a very young age. They've full filled there existential life expectancy already...

"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt." ~~ Bertrand Russell

more like arrogant
(confidence isn't so bad) the idiotic level is ignorance in the truth

Because they aren't smart enough to see and/or fear the consequences of their words/actions.

Because they aren't smart enough to know their limitations, so they believe they're capable of anything.

They can't comprehend consequences?
(Of their actions... or any inapplicability.)

Same reason smart people are I suppose. They both think they know more than they do.

They aren’t intelligent enough to see reasons to be insecure.

I'm confident I've never thought of it that way before..

They're not smart enough to know better

They don't know any better

Because y not. Lols

They don't know not to be.