The illusion of understanding

The illusion of understanding is our tendency to overestimate how well we understand things. This illusion, also known as "knowledge illusion" and "illusion of explanatory depth," occurs in all of us. 

The book The Knowledge Illusion by cognitive scientists Steven Sloman & Philip Fernbach is devoted entirely to this cognitive bias. Below I explain what this illusion entails and why it is important to know about it. 

Our world is knowledge intensive 

Humanity has built societies that are hugely knowledge intensive. This is how we distinguish ourselves as humans from other animal species. We are provided with all kinds of conveniences in our immediate vicinity. Examples of apparently simple conveniences include toilets, heaters and bicycles. Examples of more advanced conveniences are cars, cell phones and computers. 

Our wider environment is also very knowledge-intensive, such as the structure of the organizations in which we work and the way in which our society is organized, including our institutions, laws, regulations, and layers and forms of governance. 

The illusion of understanding 

Most of us can adequately find our way in these knowledge-intensive societies. We flush the toilet with ease, drive to work in our car, we file our tax returns on our computer and in the evening we watch the news on television. But cognitive scientists have found that we actually understand very little about almost all of the things we use, and much less than we think.

Three questions 

Pioneers in this field, Frank Keil and Leonid Rozenblit, did a lot of research into our ignorance. They had subjects answer three questions about things, such as zippers, toilets, watches and sewing machines. Those three questions were (with a toilet as an example here): 

  1. On a scale of 1 to 7, how well do you understand how a toilet works? 
  2. How does a toilet work? Describe in as much detail as you can all the steps in the operation of a toilet 
  3. On the same scale from 1 to 7, describe again your knowledge of how a toilet works. 

These studies invariably showed that people gave a lower score in question 3 than in question 1. The reason was that in question two they were unable to explain how the object of phenomenon in question worked at all. By being asked to explain, they discovered their ignorance. (See how a toilet works here). 

We don't realize how much we lean on external knowledge in everything we do 

Sloman & Fernbach explain that as modern people we live in communities of knowledge. Knowledge is all around us, in the machines, the systems, the organizations and in the other people. As individuals, we have become so very accustomed to continually exploiting the knowledge holders in our environment that we have a hard time realizing that that the great majority of the knowledge we use is external. 

In everything we do we make use of the combination of the knowledge in our own brain and the knowledge in our environment. And it is difficult for us to separate the two. 

Everything is more complex than we realize 

Most everything is much more complex than we normally realize. Someone who is highly educated and professionally specialized in a subject does indeed know a lot about it compared to other people. But this person, too, knows very little about infinite other things. And this person too may be hardly aware of that fact. 

Opinions on societal issues 

If you know about the illusion of understanding, you may recognize it in many conversations. For example, in the firm opinions that individuals can have about societal issues. For example, many people are making statements about what should be done with regard to the coronavirus, about whether it exists, about how dangerous it is, about what measures should or should not be taken, about how we should think about vaccines, and so on. 

I suspect that many individuals who firmly offer opinions that differ drastically from what many scientists and policymakers collectively propose do so from the illusion of understanding. I wouldn't be surprised if many of them couldn't explain in detail what a virus is, what the coronavirus is, what kind of virus it is, what a vaccine is and how it works, etc. But also I suspect they have less understanding of all kinds of social, technical, economic, administrative and logistical aspects that play a role in the crisis than they realize.


Another example of how we encounter the illusion of understanding is in our daily conversations. We often overestimate how well we understand what another person means or what their intentions are. We can then think we understand them better than we actually do. That is why we may be quick to offer advise.

But when we conduct conversations from an attitude of not knowing, we often find that what we already thought we understood about the person's situation, thoughts, or intentions was not quite right. By not filling in, but instead asking investigative questions, we often discover that their situation was different. 

What does this mean? 

Now that we know that the illusion of understanding exists, we can try to take it into account. Perhaps a first lesson should be that we can work on our modesty. Even if we ourselves are good citizens who make a admirable contribution to society, we still rely on knowledge of other people and of the devices and systems in our environment in almost all aspects of our lives. 

Perhaps a second lesson is that we can start to see almost everything in our lives as teamwork. Nobody can do anything alone. In all areas of life, we depend on bringing together the knowledge that is scattered among the different people we deal with. 

Maybe this can even be a relief. Whether we make progress does not depend on us alone. Progress always depends on bringing together distributed sources of knowledge. 

These kinds of ideas can also be found within the psychology of wisdom.