Cognitive Biases — Dunning–Kruger effect

Michael Gearon
4 min readDec 24, 2019

If you had to rate yourself 1 to 10 most people on average would rate themselves fairly high on the scale, some even as high 10. Although they may be justified in coming to that conclusion, this thought process of rating yourself highly can have negative consequences.

The Dunning-Kruger effect looks at our bias to rate ourselves higher and have a mindset that we can do something even though we may be out of our depth. The reason why it’s called “Dunning-Kruger” is because this bias became famous when two psychologists David Dunning and Justin Kruger conducted a study in 1999.

The research

William Poundstone — Dunning Kruger Effect

Dunning and Kruger produced a simple but powerful chart that illustrates this effect. It tracked competence versus confidence.

When you have no expertise whatsoever (far lower left) we can all identify that we have no competence in the matter — well, all rational people can recognise that. As Dunning and Kruger put it:

“most people have no trouble identifying their inability to translate Slovenian proverbs, reconstruct a V-8 engine, or diagnose acute disseminated encephalomyelitis.”

However, when we gain a little bit of knowledge this can become a dangerous area. Those who have a little bit of experience have greater confidence in the understanding that they “know it”. As we gain more knowledge our confidence dips dramatically. Until we actually have that in-depth knowledge then our confidence is restored, although not as highly as it was when we didn’t know it!

The below illustration shows the Dunning-Kruger effect with some labels for context:

Dunning Kruger Effect with context


Dunning and Kruger asked their 65 participants to rate how funny different jokes were. Some of the participants were exceptionally poor at determining what other people would find funny — yet these same subjects described themselves as excellent judges of humour.

Incompetent people, the researchers found, are not only poor performers, they are also unable to accurately assess and recognise the quality of their own work.

This is the reason why students who earn failing scores on exams sometimes feel that they deserved a much higher score. They overestimate their own knowledge and ability and are incapable of seeing the poorness of their performance.

Why does the Dunning-Kruger Effect happen?

Why do people overestimate themselves? Are we just too confident and overate ourselves because we don’t like to be wrong? Well, Dunning and Kruger reckon it boils down to something they call “dual burden” — that not only are we incompetent but through our incompetence our mental ability is compromised which would tell us how inept we are.

This cognitive bias effect has been documented over many years as claimed by these famous people:

“I know one thing: I know nothing” — Charles Darwin

ignorance more frequently begets confidence than does knowledge”; William Shakespeare

he who knows best knows how little he knows”. — Thomas Jefferson

Where people have little knowledge and fail, research has shown we don’t accept that we were out of our depth but instead attribute their failures to external factors. A classic example is claiming it was luck or circumstance. By doing so we protect our self-esteem instead of identifying our weakness.

The best and probably only way to prevent the Dunning-Kruger effect is to drop any inflated value of self worth. Get honest feedback and find experts in the field to benchmark yourself against. Through this self-reflection and evaluation, you can accurately work out how qualified you are in that area.

McArthur Wheeler case

While researching this cognitive bias, I came across probably one of the best examples of the Dunning-Kruger effect from 1995. Mr McArthur Wheeler had read about some peculiar properties of lemon juice, that it could be used as some sort of invisible ink.

With this in mind he decided to apply lemon juice to his face, and then proceeded to rob banks in broad daylight. He wore no mask or anything to cover his face, apart from the “invisible” lemon juice.

Obviously the security camera footage recorded him and later that day the police caught up with him and arrested him. McArthur was shocked that the police found him given that he applied the lemon juice to his face.

This shows that with only a bit of knowledge you can make some foolish errors, but if McArthur had done a little more research then he would have discovered the lemon juice would obviously not make his head disappear as the only thing it turns invisible is its own residue. What an absolute lemon.


The Dunning–Kruger effect is a really interesting cognitive bias as it is relatable. What we can take away from it is that confidence is a good thing to have but it can be detrimental unless you also have the knowledge to back it up.

Enjoyed this post on cognitive biases? Read a few more below if you’ve got 5 minutes:



Michael Gearon

Senior Interaction Designer and Co-Author to Tiny CSS Projects