What is the Dunning–Kruger effect?

If you were asked to rate how funny you are, you probably would not say you are a stand-up comedian, but still funnier than the average person. The problem? So would most people, and most of us probably just aren’t that funny.

This is the Dunning–Kruger effect, a cognitive bias brought to fame in psychologists David Dunning and Justin Kruger’s 1999 study. A common reading of it is that those people who are least competent at a task often incorrectly rate themselves as high-performers because they are too ignorant to know otherwise. You will have heard it reformulated by numerous intellectuals and writers throughout the ages:

The fool doth think he is wise, but the wise man knows himself to be a fool.”—William Shakespeare Touchstone, in As You Like It .

A little knowledge is a dangerous thing” wrote the poet Alexander Pope in An Essay on Criticism, 1709.

Charles Darwin said, “Ignorance more frequently begets confidence than does knowledge”- in The Descent of Man in 1871

Dunning and Kruger found this bias by testing students in areas of humour, grammar, and logic and compared the actual results with each student’s estimates of how well they scored. The results were that those who scored the lowest vastly overestimated their scores, while those who did best slightly underestimated their performance. It is illustrated in the graph below which shows those who are completely incompetent know it, but those with just a minimum level of competence vastly overestimate their abilities. Those who are more competent are more aware of the gaps in their knowledge, up to the point of high competence where the geniuses realise their skill level.


Source: William Poundstone

The mechanism behind this bias is two-fold. A first cause is ego. Very few people like to think of themselves as below average in anything, therefore we tend to overestimate our abilities to increase our confidence. Secondly is the more important point, which Dunning and Kruger highlight in their paper, that our below-average abilities in an area inherently makes us a bad judge of how good we are in that skill. Our knowledge gaps create difficulties in recognizing errors. It is quite hard to judge what a good writer is if you have poor grammar skills. Therefore, as Dunning and Kruger put it

overestimation occurs, in part, because people who are unskilled in these domains suffer a dual burden: Not only do these people reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the metacognitive ability to realize it.”

These people aren’t just bad at a skill, they’re also bad at knowing they are bad at it.

Why is it Important?

Human biases like overestimating our abilities can be a good way to increase our confidence but the effect can also lead people to underperform because they don’t recognise what they could be doing better, or what good performance even looks like. If we were able to recognise our failings we would be more receptive to constructive criticism and set about fixing them.


You’ve probably encountered the situation while writing an article on cognitive biases and become frustrated at how Microsoft word pastes sentences in the incorrect format or puts headings in the wrong place. However, it may be the case that you are blaming the software because you overestimate your own abilities, rather than recognising that you need further training in how to use it.

In 1995 a man robbed two banks in broad daylight without a mask or disguise. Needless to say he was arrested later that night by police who saw him smiling into the surveillance cameras. When presented with this evidence, the man was aghast, mumbling “but I wore the juice!”. The man had come to believe that lathering himself in lemon juice would make him undetectable because it is a well known fact that lemon juice is used as invisible ink.


Kruger, J., & Dunning, D. (1999). Unskilled and unaware of it: How difficulties in recognizing one’s own incompetence lead to inflated self-assessments. Journal of Personality and Social Psychology, 77(6), 1121-1134

Further Reading

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