Carlo Cipolla, a former Professor of Economics at UC Berkeley, lists the basic laws of human stupidity:
The first basic law of human stupidity asserts without ambiguity that: Always and inevitably everyone underestimates the number of stupid individuals in circulation.
At first, the statement sounds trivial, vague and horribly ungenerous. Closer scrutiny will however reveal its realistic veracity. No matter how high are one’s estimates of human stupidity, one is repeatedly and recurrently startled by the fact that:
a) people whom one had once judged rational and intelligent turn out to be unashamedly stupid.
b) day after day, with unceasing monotony, one is harassed in one’s activities by stupid individuals who appear suddenly and unexpectedly in the most inconvenient places and at the most improbable moments.
The First Basic Law prevents me from attributing a specific numerical value to the fraction of stupid people within the total population: any numerical estimate would turn out to be an underestimate. Thus in the following pages I will denote the fraction of stupid people within a population by the symbol σ.
(via @cinnamon_carter)