The Invisible Gorilla: Summary & Review

the invisible gorilla

The Invisible Gorilla is a psychology book on cognition and human biases. It builds on the most famous study on inattentive blindness and expands on the numerous ways by which our intuitions can deceive us.

Bullet Summary

  • We can’t always fully rely on our cognitive functions
  • Intuition, being based on our cognitive functions, can’t always be trusted
  • Many of us tend to overestimate our capabilities and skills -especially those with little skills!-

Full Summary

About the Authors: Daniel James Simons is an experimental psychologist, cognitive scientist, and professor of psychology at the University of Illinois Christopher F. Chabris is an American research psychologist and professor of psychology at Union College.

Second-Guess Your Intuitions

Chabris & Simon say that sometimes self-help books tell us to trust our intuitions and gut feelings.

They make the case instead that our intuitions have many limitations and we shouldn’t be trusting our “gut instincts” all that much.

This seems to be a reference to pop psychologist Malcolm Gladwell and his theory of “thin-slicing” in “Blink

We Believe We See More Than We Do

Usually, we notice what’s unusual.
But that also means that we miss a lot of what appears to be usual.

And if we are very intent on observing or paying attention to something, then we are likely to miss also something very catchy, conspicuous, and unusual.

The authors, for example, devised the gorilla experiment.

They told people to count how many times the players pass the ball to each other.
Then they would have a man dressed as a gorilla walk smack in the middle of the experiment for 9 seconds and beat his chest.
A full half of the people were so focused on counting the ball passes that they didn’t notice the gorilla.

We See What We Expect to See

Similarly, sometimes we are so focused on looking for a specific item that we fail to see anything else happening around us.

The authors say that 65% of car-motorcycle accidents happen because cars turning into driveways fail to spot the motorcycle.
It’s not that they weren’t looking, but they were looking for cars. And they failed to recognize the oncoming motorcycle.

Our Memory Is Not Accurate

The author’s survey revealed that 47% of people believe memories don’t change.
And 69% believed that memories are like videos accurately portraying all that actually happened.

But that isn’t the case.

We forget a lot, obviously.
But sometimes we also make up memories.

Some other times we remember without important details.
And other times we remember adding some details.

For example, one experiment had students read 15 associated with sleep like “slumber,” “drowsy” and “tired.”
However the word “sleep” wasn’t there, but when students were told to recite the words they read, they inserted “sleepy” in there.
That happened because we are more concerned about meaning than exact words.

Failure of Source Memory

Another interesting phenomenon related to memory is the “failure of source memory”.
That happens when people tell a story that happened to them but that actually never happened to them.

It simply happened to a friend of theirs, or they heard it a few times, and they make it their own.

Deceitful Self-Confidence

More than half of people believe they are smarter than the average.
Which of course makes little sense since 50% would be average or below.

What’s most interesting though is what came out of a survey of chess players.
Chess players are ranked internationally along with a point system. And the majority of them thought they were underrated by at least 100 points.
And the interesting point: the lower the skills of the players, the more they thought they overestimated their skills.

More Confidence Doesn’t Mean More Skills

But unluckily, the more people act self-confident, the more they tend to believe and trust their skills and knowledge.

A famous experiment at the University of Rochester showed that doctors that gave a prescription without looking up the disease were rated as more trustworthy than doctors who didn’t look up the disease.
But the doctors who took the time to double-check were right more often.

This is one of the reasons why charismatic men tend to draw such a major following: they look secure and people trust them.

We Know Less Than We Think We Do

The more we are familiar with something, the more we believe we “know” it.

However most people failed to accurately depict the functioning of a bike, and probably most of us have no idea how a toilet actually works.

We also tend to overestimate our understanding of a topic if we receive lots of information about it.

However, lots of information can often lead us astray as we get lost in the noise of the short term -also read The Signal and the Noise-.

We See Causation Where There Is None

Humans look for patterns.
And end up seeing a lot of them. Often, where there are no patterns at all.

We are most at risk of seeing non-existing patterns when two events happen at the same time.
Then our brain immediately goes “ah, this happened, it must be because of that”.

Also, read:

the invisible gorilla

The Invisible Gorilla Video

This is a video of the famous experiment.
Half of the people who were instructed to count the ball passes hadn’t noticed there was a gorilla walking right in the middle of that group.

Real-Life Applications

  • Beware of Over-Confident Individuals

Those who looked overly confident are either really well prepared or… They might just be super wrong.

  • Don’t Trust Those Who Believe They’re Underrated & Underappreciated

It’s often those with the lowest skill level to believe they deserve more and that they are being unfairly judged.
Of course, also keep in mind this might not always be the case and of course, many can indeed be unfairly judged.


  • Needless War on Intuition?

The authors take aim at intuition right from the title.
However, the biases they talk about do not necessarily disprove intuition or its usefulness.
It feels that it’s an unneeded war against intuition. And, at the end of “The Invisible Gorilla“, there is no strong case against intuition.

  • Too Long

The invisible gorilla experiment was an interesting one, and the other experiments the authors describe are also interesting.
But it feels padded and “The Invisible Gorilla“, the book, could have all been briefer


Some Good Insights
Even as an avid reader of psychology, I learned a couple of good things. Like why so many cars fail to see motorcycles.


The Invisible Gorilla builds on a famous experiment to make a larger case on human cognition and biases.

For most people with a keen interest in psychology, some of the content will not be new.
But I found a few new tidbits here and there.

Check the best psychology books or get the book on Amazon

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