, understanding
, reason
, wit
, or sense
. It may be innate, assumed, or reactive - 'being "stupid with grief" as a defence against trauma
', a state marked with 'grief and despair...making even simple daily tasks a hardship'.
Oeijord, in his critique of Stephen Jay Gould
, argued that 'creative stupidity and able misfits prove the existence of the human learning instincts...[that] can exist because instincts are highly independent'.
Stupidity is a quality or state of being stupid, or an act or idea that exhibits properties of being stupid.
A fool's mind is at the mercy of his tongue and a wise man's tongue is under the control of his mind. 
I never heard tell of any clever man that came of entirely stupid people.
Aristotle taught that the brain exists merely to cool the blood and is not involved in the process of thinking. This is true only of certain persons.
Never attribute to malice that which is adequately explained by stupidity.
"Folly is as great as the sea. It can compass anything."
A person is smart. People are dumb, panicky, dangerous animals and you know it.
There is no sin except stupidity.
Weapons-Grade Stupidity: Tech-support slang for customer intelligence that is so low it poses a severe hazard to those who come in contact with it.