“The fool doth think he is wise, but the wise man knows himself to be a fool,” wrote Shakespeare in As You Like It. Little did he know, but this line perfectly encapsulates the spirit of the Dunning-Kruger effect.

The Dunning-Kruger effect is a cognitive bias first highlighted in literature by David Dunning and Justin Kruger in the (now-famous) 1999 study Unskilled and unaware of it: How difficulties in recognizing one’s own incompetence lead to inflated self-assessments.

The study was borne from the shenanigans of one McArthur Wheeler who, in the broad daylight of a sunny April 19, 1995, decided to rob two saving banks in Pittsburgh. Wheeler carried a gun, but not a mask. Surveillance cameras recorded him in the act, and the police put his picture up in local news, receiving multiple tips almost immediately.

When they went to perform the arrest, Mr. Wheeler was visibly confused.

“But I wore the juice,” he managed, before officers carried him away.

There’s no such thing as ‘foolproof’

At one point in his life, Mr. Wheeler learned that lemon juice can be used as an ‘invisible ink’. Write something down on a piece of paper using lemon juice and you won’t see a thing — until you heat it up, making the scribblings visible. So, naturally, he covered his face in it and went to rob a bank, confident that his identity would remain secret to cameras as long as he didn’t come close to any sources of heat.

Still, credit where credit is due: Mr. Wheeler wouldn’t go out on blind faith. He actually did test out his theory by taking a selfie with a polaroid camera (there’s a budding scientist in all of us). For some reason or another, maybe the film was defective, we don’t know exactly why, the camera did return a blank image.

The news made the rounds, everybody had a good chuckle, and Mr. Wheeler was wheeled off to jail. The police concluded that he wasn’t crazy or on drugs, he actually believed his plan would work. “During his interaction with the police, he was incredulous on how his ignorance had failed him,” wrote Anupum Pant for Awesci.

David Dunning was working as a psychologist at Cornell University at the time, and the bizarre story caught his eye. Enlisting the help of Justin Kruger, one of his graduate students, he set out to understand how Mr. Wheeler could be so confident in a plan that was plainly stupid. The theory they developed is that almost all of us view our abilities in certain areas as above average and that most are likely to assess our skills as being much better than they objectively are — an “illusion of confidence” that underpins the Dunning-Kruger effect.

We’re all clueless

“If you’re incompetent, you can’t know you’re incompetent,” Dunning wrote in Self-Insight: Roadblocks and Detours on the Path to Knowing Thyself.

“The skills you need to produce a right answer are exactly the skills you need to recognize what a right answer is.”

In the 1999 study (the first they carried out on the topic), the duo asked undergrads at Cornell a series of questions about grammar, logic, and humor (these were used to gauge the students’ actual skills) and then asked each to estimate the overall score they would achieve, and how that related to the scores of the other participants. The lowest-ranking students, they found, consistently and substantially overestimated their own ability. Students in the bottom quartile (lowest 25% by score) thought that they out-performed two-thirds of the other students on average (i.e. that they ranked in the top 33% by score).

A follow-up study that the authors carried out at a gun range showed similar results. Dunning and Kruger used a similar methodology, asking hobbyists questions about gun safety and to estimate how well they performed on the quiz. Those who answered the fewest questions correctly also wildly overestimated their mastery of firearm knowledge.

It’s not specific only to technical skills but plagues all walks of human existence equally. One study found that 80% of drivers rate themselves as above average, which is literally impossible because that’s not how averages work. We tend to gauge our own relative popularity the same way.

It isn’t limited to people with low or nonexistent skills in a certain matter, either — it works on pretty much all of us. In their first study, Dunning and Kruger also found that students who scored in the top quartile (25%) routinely underestimated their own competence.

A fuller definition of the Dunning-Kruger effect would be that it represents a bias in estimating our own ability that stems from our limited perspective. When we have a poor or nonexistent grasp on a topic, we literally know too little of it to understand how little we know. Those who do possess the knowledge or skills, however, have a much better idea of where they sit. But they also think that if a task is clear and simple to them, it must be so for everyone else as well.

A person in the first group and one in the second group are equally liable to use their own experience and background as the baseline and kinda just take it for granted that everyone is near that baseline. They both partake in the “illusion of confidence” — for one, that confidence is in themselves, for the other, in everyone else.

But perhaps not equally clueless

To err is human. But, to confidently persist in erring is hilarious.

Dunning and Kruger did seem to find a way out of the effect they helped document. While we all seem to be equally likely to delude ourselves, there is one key difference between those who are confident yet unable and those able yet lacking in confidence — how we deal with and integrate feedback into our behavior.

Mr. Wheeler did try to check his theory. Yet, he looked at a blank polaroid he just shot — a pretty big giveaway that something didn’t work out properly — and saw no cause for concern; the only explanation he accepted was that his plan worked. Later, he receives feedback from the police, but this in no way shape or form manage to diminish his certainty; he was “incredulous on how his ignorance had failed him” even when he had absolute confirmation (being in jail) that it did fail him.

During their research, Dunning and Kruger found that good students would better predict their performance on future exams when given accurate feedback about the score they achieved currently and their relative ranking among the class. The poorest-performing students would not change their predictions even after clear and repeated feedback that they were performing badly. They simply insisted that their assumptions were correct.

Jokes aside, the Dunning-Kruger effect isn’t a failing on our part; it’s simply a product of our subjective understanding of the world. If anything, it serves as a caution against assuming we’re always right and highlights the importance of keeping an open mind and a critical view of our own ability.

But if you’re afraid that you might be incompetent, you could check by seeing how feedback affects your view on your own work, knowledge, skills, and how that relates to others around you. If you truly are, you won’t change your mind and this process is basically a waste of time but fret not — someone will tell you you’re incompetent.

And you won’t believe them.