Cipolla's five fundamental laws of stupidity:

1. Always and inevitably everyone underestimates the number of stupid individuals in circulation.
2. The probability that a certain person (will) be stupid is independent of any other characteristic of that person.
3. A stupid person is a person who causes losses to another person or to a group of persons while himself deriving no gain and even possibly incurring losses.
4. Non-stupid people always underestimate the damaging power of stupid individuals. In particular non-stupid people constantly forget that at all times and places and under any circumstances to deal and/or associate with stupid people always turns out to be a costly mistake.
5. A stupid person is the most dangerous type of person.