In the middle of the 20th century, the field of psychology had a problem. In the wake of the Manhattan Project and in the early days of the space race, the so-called “hard sciences” were producing tangible, highly publicized results. Psychologists and other social scientists looked on enviously. Their results were squishy, and difficult to quantify.
Psychologists in particular wanted a statistical skeleton key to unlock true experimental insights. It was an unrealistic burden to place on statistics, but the longing for a mathematical seal of approval burned hot. So psychology textbook writers and publishers created one, and called it statistical significance.