Dunning Kruger effect is a psychological syndrome where dumb people overestimate their own intelligence (and conversely, very smart people downplay their own).
Barack Obama is the quintessential example of this. As a rule, people who tout themselves as the smartest in the room are usually the stupidest.
Unfortunately, the dim-witted person, by overestimating their own ability, actually becomes dumber and dumber by not realizing what they need to learn. They handicap themselves through a sort of wilful ignorance, shutting out new information because they believe they already know it all.
As we saw with Obama, the fiercely ignorant person becomes a laughingstock because everyone except him sees his own idiocy.