Now try this before you read on: picture a simple sketch of a bicycle frame, two wheels, pedals and chain. Where does the chain go? Which parts does the frame connect?
When psychologist Rebecca Lawson tested people's understanding of basic bicycle design in 2006, many made frequent and serious mistakes, such as believing the chain went around the front wheel as well as the back one, which would make the bike impossible to steer. Bicycle experts made fewer errors but still made some, and so did people who had a real bicycle in front of them during the test.
That's not a story about bicycles. It's about a gap almost everyone has between feeling that we understand something and actually understanding it.
The illusion of explanatory depth
In 2002, psychologists Leonid Rozenblit and Frank Keil of Yale University gave the gap a name: the illusion of explanatory depth. In a series of twelve studies, they asked people (Yale undergraduates) to rate how well they understood how various devices worked, then to write a detailed explanation of how each one works, and then to rate their understanding again. Ratings dropped once people tried to explain. They had mistaken familiarity for knowledge.
Two of their findings are especially useful:
- The illusion is strongest for explanations, knowledge of how things work, and much weaker for facts (a country's capital), procedures (how to make a dish) or stories (the plot of a film). It's easy to check whether you know a fact. It's hard to notice that your "explanation" is a blank with a label on it.
- It's strongest for things with visible parts. When you can see the pieces of something move, like a bicycle's chain and gears, it feels as if seeing them means understanding them.
Knowing what something is called, or how to use it, is not the same as knowing how it works. The feeling of understanding doesn't tell those apart.
This is related to, but different from, the Dunning–Kruger effect (see The Biases That Fool Everyone, this category). Dunning–Kruger is about beginners misjudging their skill. The explanatory-depth illusion hits nearly everyone, experts included, outside their own narrow specialty, and often inside it.
Why our brains get away with it
Partly, it's efficient. You don't need to understand a fridge's refrigeration cycle to keep milk cold. Cognitive scientists Steven Sloman and Philip Fernbach argue in The Knowledge Illusion that human knowledge mostly lives in communities, in other people, books, tools and the world itself, rather than in any single head. We get by because someone, somewhere, does understand the fridge. The trouble starts when we forget that the understanding is borrowed, and act as though it were our own.
Where it costs us: opinions
That's where the illusion stops being harmless. In 2013, Fernbach and colleagues asked people about complex political policies they felt strongly about. People rated their understanding, then were asked to explain, step by step, how the policy would actually work. Their ratings of their own understanding fell, and their opinions became more moderate.
The detail that matters most: when people were instead asked to list the reasons for their position, their views didn't soften. Arguing for a view doesn't expose the gaps. Explaining the mechanism does. In a third experiment, people who had explained a policy were also less willing to donate to advocacy groups on that issue.
That's a sobering finding for anyone who argues about politics, health or economics online. Our strongest opinions are often about systems we couldn't explain in a paragraph.
How to test yourself
The fix is simple and slightly uncomfortable: try to explain it. Not "summarize it" or "argue for it," but explain how it works, step by step, as if to a curious 12-year-old who keeps asking "and then what?"
Write it down. Explanations in your head skip steps without telling you. On paper, the gaps show up as the place where you stop being able to write the next sentence.
Use "how," not "why." "Why is inflation bad?" invites reasons. "How does printing money raise prices, step by step?" exposes whether you know the mechanism.
Mark the borrowed parts. When you hit something you can't explain, label it: "I'm trusting experts here." That's fine and usually unavoidable. It just changes how confidently you should talk about it.
This is close to what's often called the Feynman technique, explaining something in plain language to find what you don't understand (covered as a study tool in How to Learn Anything Faster, this category). Here the point is broader: it's a check on your confidence in everything, not just in what you're studying.
The honest limits
You can't verify everything yourself, and you shouldn't try; relying on trustworthy expertise is a reasonable way to live. The goal isn't to understand every system. It's to know which of your beliefs you actually understand and which you're borrowing, and to hold the borrowed ones a little more loosely. The research also has limits: it rests on a fairly small set of studies, and the effect on opinions was a moderation, not a conversion. Explaining things won't make people agree. It tends to make them less certain, which is often the beginning of thinking well.
The takeaway
Most of us feel we understand how things work far better than we do, an effect called the illusion of explanatory depth. It's strongest for explanations of mechanisms, especially ones with visible parts, and it extends to political and economic opinions, which grow more moderate when people try to explain how a policy would actually work. The best test is to explain something step by step, in writing, using "how" rather than "why," and to mark honestly which parts of your understanding are borrowed from others.
Try this: pick an opinion you hold strongly about a policy or a technology. Write, step by step, how it actually works or would work, without arguing for your side. Notice where you get stuck, and whether your certainty changes.
Sources & Further Reading
Sources
- Rozenblit L. & Keil F., "The misunderstood limits of folk science: An illusion of explanatory depth," Cognitive Science 26 (2002).
- Lawson R., "The science of cycology: Failures to understand how everyday objects work," Memory & Cognition 34 (2006).
- Fernbach P. M., Rogers T., Fox C. R. & Sloman S. A., "Political extremism is supported by an illusion of understanding," Psychological Science 24 (2013).
- Sloman S. & Fernbach P., The Knowledge Illusion: Why We Never Think Alone (2017).
Go deeper
- 📘 The Knowledge Illusion: Why We Never Think Alone — Steven Sloman & Philip Fernbach (the full argument, readable and funny)
- 📘 The Scout Mindset — Julia Galef (on wanting to see things as they are, not as you'd like them to be)
- 🌐 See also, in this category: How to Spot Bullshit and The Biases That Fool Everyone