The Müller-Lyer illusion symbolizes people’s inability to change how they process information, even when they know they are wrong. The Müller-Lyer illusion is an image: on the top is a horizontal line with arrows or fins attached to it that point outward, away from the line. On the bottom is another horizontal line with arrows or fins that point inward, towards the line. Measuring would reveal that the two horizontal lines are the same, but the horizontal line in the bottom figure always appears longer. Even though we learn that the two lines are equally long, that is not our automatic intuition about them.
This illusion then becomes a good stand-in for what Kahneman calls “cognitive illusions.” Like the Müller-Lyer illusion, there are cognitive illusions in which, even though people learn what the real answer to a puzzle might be, their intuition will still tell them that a different answer is the correct one. Kahneman’s purpose in writing the book, then, is to help people learn the illusions—like Müller-Lyer—in which they might make a mistake, and to remind them to expend a little more effort in calculating their answers and making decisions.
Müller-Lyer Illusion Quotes in Thinking, Fast and Slow
The set of feminist bank tellers is wholly included in the set of bank tellers, as every feminist bank teller is a bank teller. Therefore the probability that Linda is a feminist bank teller must be lower than the probability of her being a bank teller. […] The problem therefore sets up a conflict between the intuition of representativeness and the logic of probability.
The illusion of skill is not only an individual aberration; it is deeply ingrained in the culture of the industry. Facts that challenge such basic assumptions—and thereby threaten people’s livelihood and self-esteem—are simply not absorbed.