The power of flaws was first discovered in 1966 by Harvard University psychologist Elliot Aronson. In his experiment Aronson recorded an actor answering a series of quiz questions. In one strand of the experiment, the actor – armed with the right responses – answers 92% of the questions correctly. After the quiz, the actor then pretends to spill a cup of coffee over himself (a small blunder, or pratfall).
The recording was played to a large sample of students, who were then asked how likeable the contestant was. However, Aronson split the students into cells and played them different versions: one with the spillage included and one without. The students found the clumsy contestant more likeable.
Aronson called this insight the pratfall effect.