Stupidity is the inability to discern the essential from the accidental: it consists in attaching oneself to mere facts and in considering them simply in themselves, that is, without the least induction. (GTUFS: EyeHeart, Transgression and Purification)
It is not without reason that popular opinion tends to associate pride with STUPIDITY. One can in fact be pretentious through STUPIDITY just as one can be stupid through pretension; the two things go together. Of course, lack of intelligence does not necessarily lead to pretension, but pretension cannot avoid harming the intelligence. And if, as is commonly admitted, STUPIDITY is the incapacity to discern between the essential and the secondary, or between cause and effect, it includes for that very reason a measure of pride; a STUPIDITY combined with a perfect humility and a perfect detachment would no longer be STUPIDITY, it would be a simplicity of mind which could trouble no intelligent and virtuous person. (GTUFS: SurveyME, Passion and Pride)
Let us specify that STUPIDITY often manifests itself through confusion between a material cause and a moral cause, or between a phenomenon due to circumstances and another resulting from a fundamental quality, in short, between an “accident” and a “substance”; for example, a government is taken for a people, or a collective psychosis for an ethnic character. (GTUFS: HaveCenter, Intelligence and Character)