Most books and articles about cognitive bias contain a brief passage, typically toward the end, similar to this one in Thinking, Fast and Slow: “The question that is most often asked about cognitive illusions is whether they can be overcome. The message … is not encouraging.”Kahneman and others draw an analogy based on an understanding of the Müller-Lyer illusion, two parallel lines with arrows at each end. One line’s arrows point in; the other line’s arrows point out. Because of the direction of the arrows, the latter line appears shorter than the former, but in fact the two lines are the same length. Here’s the key: Even after we have measured the lines and found them to be equal, and have had the neurological basis of the illusion explained to us, we still perceive one line to be shorter than the other.
At least with the optical illusion, our slow-thinking, analytic mind—what Kahneman calls System 2—will recognize a Müller-Lyer situation and convince itself not to trust the fast-twitch System 1’s perception. But that’s not so easy in the real world, when we’re dealing with people and situations rather than lines.
“Unfortunately, this sensible procedure is least likely to be applied when it is needed most,” Kahneman writes. “We would all like to have a warning bell that rings loudly whenever we are about to make a serious error, but no such bell is available.”