The Dunning-Kruger effect in psychology is a bias among people (men?) of low skill. They consistently over-estimate their abilities. Perhaps because of their low skill/knowledge in a field they don’t even realize just how poor theirs is. And their over-estimation gives them more confidence.
And many people are attracted to people with high confidence. Someone who says “I know what to do!” is generally more convincing and appealing than someone who says “It’s complex. I will have to think about that and get back to you.”