cognitive psychology
Dunning-Kruger effect
What is the Dunning-Kruger effect?
The Dunning-Kruger effect is the gap between how good people think they are and how good they actually are - widest at the bottom, where knowing too little to spot your own mistakes leaves you oddly confident. The less you know, the less you know it.
Also known as: Dunning Kruger, illusory superiority, confidence-competence gap
The demo
One short question. Rate how sure you are before you answer - then see how your confidence lines up with whether you actually got it right.
A bat and a ball cost £1.10 together. The bat costs £1 more than the ball. How much is the ball?
Rate your confidence to begin.
What this demo shows (text version)
A trick question is posed: a bat and a ball cost £1.10 together, and the bat costs £1 more than the ball, so how much is the ball? You first rate how confident you are, then choose an answer.
The intuitive answer is 10p, and it is wrong - if the ball were 10p the bat would be £1.10, making £1.20 in total. The ball is 5p (the bat £1.05). The demo compares your stated confidence with whether you were right. The point of the Dunning-Kruger effect is that the people most likely to feel sure here are often the ones who have not spotted the trap - high confidence and low accuracy arriving together.
You answered fast and felt sure - the question seemed easy. It seemed easy because you could not see what you were missing: the same gap that produced the wrong answer also hid that it was wrong. Real expertise tends to feel less certain, not more.
It cuts both ways. Beginners overrate themselves because they lack the knowledge to judge their own work; genuine experts often underrate themselves, assuming what is now obvious to them is obvious to everyone. So loud confidence is a weak signal of skill - and occasionally the opposite of it.
In product work it is the stakeholder certain a design is "intuitive" because they already know how it works, and the new user who cannot find the button. The cure is the usual one: test with real people, and treat your own certainty as a hypothesis rather than a verdict.