What is Stupidity?

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Just as the mother in the book by Lionel Shriver says “We need to talk about Kevin”, we need to talk about stupid.
A stupid person is described in the Merriam-Webster Dictionary as slow of mind, lacking intelligence and reason, dulled in feeling and sensation, senseless and lacking interest or point.

Most of you must have heard by now of the Dunning-Kruger Effect: it is when people with limited knowledge or competence coupled with cognitive bias greatly overestimate their own knowledge or competence because they lack the expertise required to recognize their own incompetence. Conversely, experts may underestimate their competence, assuming tasks easy for them are easy for others.

So, why do we need to talk about ~~Kevin~~, stupidity?

Because as Dietrich Bonfoeffer, a German theologian and anti-Nazi dissident wrote before he was hanged by the Nazis, stupidity is a more dangerous enemy of good than malice.
"One man alone can be pretty dumb sometimes, but for real bona fide stupidity, there ain't nothin' can beat teamwork" - Edward Abbey

"Some ideas are so stupid that only intellectuals believe them" - George Orwell

"Half the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm (that they cause) does not interest them. Or they do not see it, or they justify it because they are absorbed in the endless struggle to think well of themselves" T.S Eliot.

"The U.S is the leader of stupid" - Jeffrey Sachs, economist & public policy analysis, professor at Columbia U.

That last quotation should worry the world aplenty.
Ignorance of history, knowledge and lack of a deep understanding of how the world works can lead to unnecessary trade wars and armed global conflicts.

We should try to understand Stupidity because it is a danger to everyone. It is not just practiced by the uneducated, the ignorant, but also the educated, the doctors, teachers, scientists, lawyers, industrialists, politicians, the intellectuals. It is not necessarily the lack of intelligence but the surrender of it, the surrender of independence. But why do seemingly smart people surrender their intelligence and ignore the obvious, facts, evidences? Why do we surrender to stupidity?
Who is more dangerous, an evil and smart man or the stupid man? "Stupidity and human incompetence are the great evils, not ambition and glory" - Robert Green.
Do you agree?

We need to talk about stupidity lest we should be stupid.
What is stupidity to you?