The Dunning–Kruger Effect

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There’s something deliciously ironic about the Dunning–Kruger effect. The very people most affected by it are the least likely to recognise it. Like a man who proudly boasts of his poker face while holding his cards the wrong way round. But the phenomenon—first coined in 1999 by social psychologists David Dunning and Justin Kruger—is more than a punchline. It’s a quiet, persistent force that shapes our conversations, our workplaces, our politics, and yes, our sales meetings.

In simple terms, the Dunning–Kruger effect describes a cognitive bias where people with low ability at a task overestimate their ability. They don’t know enough to know what they don’t know. It’s not arrogance—though it can present that way—it’s ignorance disguised as confidence. And it’s everywhere.

In their original study, Dunning and Kruger asked participants to complete tests in humour, grammar, and logic. Those who scored in the bottom quartile consistently rated their performance far higher than it actually was—some placing themselves in the top decile. In contrast, the top performers tended to underestimate their own competence, assuming others found the tests just as easy as they did. It was a double-blind disaster: the unskilled didn’t realise their own lack of skill, and the highly skilled didn’t realise how exceptional they were.

Since then, the effect has been replicated in a range of settings—from academic exams to chess to medical diagnosis. One study published in the Journal of Personality and Social Psychology found that 88% of American drivers believed themselves to be above-average behind the wheel. Which is statistically impossible, unless the bottom 12% are all hiding in a layby somewhere.

But it’s not just a statistical curiosity. The Dunning–Kruger effect plays havoc in teams and organisations. It fuels overconfident managers, under-qualified applicants, and painfully drawn-out Zoom calls led by people who mistake volume for insight. It creates blind spots in strategy meetings and makes training initiatives harder than they should be—because the people most in need of learning don’t think they have anything left to learn.

It also explains why debates so often feel like ships passing in the night. The louder voice isn’t always the better-informed one. And as anyone who’s ever watched an all-hands meeting descend into chaos will tell you: confidence is not a proxy for competence.

Still, there is something oddly comforting in the levelling power of the Dunning–Kruger effect. It cuts both ways. Just as it inflates the unskilled, it suppresses the skilled. High performers tend to assume their abilities are common. They don’t realise their instinct for pattern recognition or their emotional intelligence or their deft handling of nuance is, in fact, rare. They quietly excel, often to their own surprise, while others bluster and bluff.

How it affects learning

The Dunning–Kruger effect doesn’t just distort how we see ourselves—it actively gets in the way of growth. When someone believes they’ve already mastered a topic, their appetite for learning dries up. Why seek out feedback when you think you’re already an expert? Why read the manual when you’re convinced you’ve got the knack?

This false sense of competence is particularly corrosive in environments where self-direction is required. A study from Cornell University found that people who scored lowest on logical reasoning tests were also the least likely to seek help or improve their performance on subsequent attempts. Not because they were lazy—but because they genuinely thought they were doing fine.

On the other hand, those who scored highest were often the most self-critical. They actively looked for errors in their thinking, adjusted their approach, and improved more quickly over time. In essence, the better you are, the more you’re likely to know how much better you could be. It’s the intellectual equivalent of standing on a mountain and suddenly seeing the range stretch out ahead of you.

In learning environments, this creates a quiet chasm between those who believe they’re growing and those who actually are. The loudest learner in the room isn’t always the one learning the most. And until someone becomes aware of what they don’t know, no amount of training will land. Recognition must come before revelation.

How it affects sellers

Sales is one of the most visible arenas where the Dunning–Kruger effect plays out. New or underperforming reps often overestimate their ability because they’ve not yet grasped the depth of skill the job requires. They think selling is about talking, persuading, controlling the call. They conflate energy with effectiveness. The worst ones interrupt you to prove they’re listening.

But the effect doesn’t just apply to the struggling. It can trip up decent sellers too—especially those who think they’ve “cracked it.” A few good quarters, a handful of big deals, and suddenly the curiosity vanishes. The learning stops. The seller assumes they know what works, and doubles down on it. They stop listening to coaching, stop adapting to buyers, and start sleepwalking through calls. Slowly, their competence calcifies. The very belief that they’re already great becomes the thing that stops them getting better.

In modern sales—where buyer expectations shift faster than playbooks can keep up—the Dunning–Kruger effect is a silent career killer. The top performers I meet aren’t the cocky ones; they’re the curious ones. They’re still refining, still listening to call recordings, still open to the idea that they might be wrong. Confidence can win you a first meeting. But humility, oddly enough, is what gets you the next one.