The Barnum or Forer effect is the tendency for people to judge that general, universally valid statements about personality are actually specific descriptions of their own personalities. A "universally valid" statement is one that is true of everyone—or, more likely, nearly everyone. It is not known why people tend to make such misjudgments, but the effect has been experimentally reproduced.
The psychologist Paul Meehl named this fallacy "the P.T. Barnum effect" because Barnum built his circus and dime museum on the principle of having something for everyone. It is also called "the Forer effect" after its discoverer, the psychologist Bertram R. Forer, who modestly dubbed it "the fallacy of personal validation".