After Learning About 100 Cognitive Traps, I Grew Fond of My Own 'Assumptions'

I have a question for you, if I may.

How much confidence do you have in your own judgment?

"I think I'm a fairly rational thinker"—if that was your answer, I was actually the same way. In my medical practice, I strive to make evidence-based decisions every day, and as a licensed psychologist, I felt I had learned a reasonable amount about how the human mind works.

However, one day I came across a website called "Cognitive Illusion Collection 100", and I honestly laughed at how many "thinking habits" I had within me. After laughing, I felt a little shudder, and in the end, I even felt a strange sense of relief, thinking, "Well, it's because of these habits that I am who I am."

This time, I would like to introduce this wonderful resource, the "Cognitive Illusion Collection 100," from the perspective of someone involved in medicine.

What is a "Cognitive Illusion"?—A New Term for Thinking Illusions

Are you familiar with the term "optical illusion"? It refers to the phenomenon where your vision is deceived, such as when lines of the same length appear to be different, or a still image appears to be moving.

"Cognitive illusion" is the thinking version of that. In other words, it is a coined term that refers to "illusions of thought = cognitive biases." It was named by a team includingMasami Ikeda of Jumonji University, and the site that systematically collects these "illusions of the mind," rather than illusions of the eyes, is the "Cognitive Illusion Collection 100".

I thought this naming was fantastic. When you say "cognitive bias," it sounds like something out of an academic paper, but when you call it a "cognitive illusion," it immediately clicks as "Oh, you mean assumptions." Plus, since it can be remembered as a set with "optical illusion," it's hard to forget once you hear it. There is one more important nuance included here, which is the perspective that"bias does not equal evil".

Optical illusions are things you enjoy while laughing, "I've been tricked!" In the same way, you should just learn that thinking habits are "how things work" and learn to get along with them. The site's production team also states this: there are aspects where having biases helps prevent unnecessary anxiety and depression, and helps maintain composure and self-esteem.

I realize this when I'm in a clinical setting. For example, the "optimism bias"—the mental habit of assuming "I'll be fine." From a disaster prevention perspective, this is a dangerous bias, but if it didn't exist at all, people would be crushed every day by the anxiety that "I might get into a traffic accident" or "I might get a serious illness." Biases are also "shields" that protect our minds.

The Big Picture of the Site—Let's Walk Through the 3 "Exhibition Rooms"

The "Cognitive Illusion Collection 100" was born as an outreach project for full-scale research funded by a KAKENHI grant from the Japan Society for the Promotion of Science. 100 cognitive biases are introduced, divided into three categories (called "exhibition rooms" on the site).

First is "cognitive biases related to memory". This is an area that confronts us with how unreliable our memories are and how easily they can be rewritten. Next is "cognitive biases related to decision-making and beliefs". This reveals how our judgments are distorted, from daily choices to major life decisions. And finally, "cognitive biases related to others and the self". This lists assumptions related to interpersonal relationships and self-perception.

Of course, one bias doesn't fit neatly into one category, and I feel it's honest and good that the site itself clearly states that "the classification is just a broad framework."

Each bias page is composed of four common parts. A "catchphrase" that succinctly expresses the characteristics of that bias, "for example" which depicts a concrete daily scene, "let's think about it" for the reader to consider themselves, and "explanation" which introduces the definition, mechanism, and research results. This flow is very well-made, and it is designed so that after intuitively feeling "that happens!", you can read the scientific backing to realize the "discrepancies" within yourself.

"Memory" is not as accurate as you think

Among the biases related to memory, the one that particularly surprised me was "false memory". The catchphrase is "Did that really happen?". It is a phenomenon where you "remember" an event that didn't actually happen as if you had experienced it.

This is a serious problem in the medical field. The progress of symptoms described by a patient, such as "when it started" and "how it happened," is the basis for diagnosis. But there is a possibility that the memory itself has transformed without the person even realizing it. The "post-event information effect"—in other words, the original memory can be rewritten by information obtained after the event (knowledge researched on the internet, hearsay from family, etc.). Just knowing this changes how I conduct medical interviews.

"Rosy retrospection" is also interesting. The catchphrase is "I want to go back to that day," and it refers to the tendency to remember past events more beautifully than they were at the time. When a patient says, "They treated me better at the previous hospital," is that an objective fact, or is it a memory painted in rosy colors? Of course, I don't mean to belittle the patient's words, but just knowing this tendency adds depth to how I receive them.

Let me introduce one more: Reminiscence Bump. As the catchphrase 'only memories of student days' suggests, there is a tendency for memories from one's teens and twenties to remain particularly vivid throughout life. That moment when an elderly patient's eyes suddenly light up when talking about their youth—realizing that this is backed by a brain mechanism where 'there are memories that are easier to recall' helps me understand the significance of reminiscence therapy and life review much more deeply.

"Invisible forces" that distort judgment—decision-making biases

Biases related to decision-making might be the area where we feel the effects most strongly in daily life, business, and even medicine.

Let's take Anchoring as an example. This bias, described as 'being bound by what you learned first,' is a phenomenon where judgment is dragged along by the first number or piece of information presented. For instance, a person who hears a reference value for a test result as '50' first and someone who hears '100' first will perceive the same test result differently. We are influenced by the 'first information we encounter' far more than we think.

The Framing Effect is connected to medicine even more directly. 'The success rate of this surgery is 90%' versus '1 in 10 people die from this surgery'—mathematically, they are saying exactly the same thing, but the latter feels much scarier, doesn't it? This is not just a matter of technique, but an issue involving the ethics of how we communicate information as medical professionals.

Personally, the one that made me slap my knee and say 'that's so true' was the Sunk Cost Effect. The catchphrase 'what a waste' is brilliant. It is a bias where you are dragged along by costs that can no longer be recovered—time, money, effort—and become unable to make a rational withdrawal. In a medical setting, this sometimes appears as continuing a treatment that is not effective simply because 'we have been using this treatment plan until now.' I myself have had the experience of continuing an approach that should have been reviewed because 'I've already spent this much time on it.' It's a painful story, but that is precisely why I think it is important to name it and be aware of it.

I also want you to know about the Present Bias—'Fifty today is better than a hundred tomorrow.' It is the tendency to overvalue small, immediate gains over large, future ones. I think many people can relate to the psychology of procrastinating by saying, 'Even if an abnormality is found in my health checkup, I'm busy now, so I'll do it next month.'

Assumptions lurking in human relationships

The biases regarding others and the self were the ones that 'stung' the most while reading.

The Self-Serving Bias—success is thanks to my own ability, failure is the fault of the environment or luck. The Fundamental Attribution Error—tending to think others' failures are due to their personality, while explaining one's own failures as 'the situation was bad.' If you remember these two as a set, the way you see human relationships in the workplace will change completely.

I couldn't help but laugh at the catchphrase 'Do horoscopes work!?' for the Barnum Effect. It is the phenomenon of feeling that vague descriptions that apply to anyone are 'perfect for me.' This is one of the reasons why blood-type personality diagnosis is so deeply rooted in Japan. As someone with a certified public psychologist qualification, I can say that there are quite a few things that call themselves psychological tests or personality diagnoses that have little scientific basis. Knowing about the Barnum effect is also a way to gain 'immunity' against such information.

The Spotlight Effect—the bias that 'everyone is looking at me' is also interesting. In reality, others don't care that much about your failures or appearance, but the person themselves overestimates that they are 'being watched.' That feeling when you stumble during a presentation or notice a stain on your shirt and assume 'everyone saw it...' In fact, the people around you hardly notice. Just knowing this should make your daily anxieties much lighter.

And Victim Blaming is a socially very important bias. It is the tendency to think that the victim 'must have been at fault in some way,' and behind it is the belief that 'the world is fair' (Just-World Hypothesis). This can be directed at disaster victims, crime victims, and even patients who have become ill. There is a possibility that this cognitive bias is at work behind the words, 'Your lifestyle habits were bad, weren't they?' As a medical professional, I think it is very important to be aware of this mechanism.

Why is it important to 'know about cognitive biases' now?

There are stories here that would be a waste to just finish by saying, 'Huh, that's interesting.'

The modern era is an age of information overload. A vast amount of information flows through SNS timelines every day, and fake news and conspiracy theories are mixed in. The Illusion of Truth—the bias where information heard repeatedly feels 'true' regardless of its veracity—is truly a pitfall of the SNS era. As you see the same claim over and over, you feel, 'Since so many people are saying it, it must be true.' But that may not be a judgment based on evidence, but merely a 'repetition effect.'

The Confirmation Bias is also dangerous. You collect only information that fits your beliefs and ignore information that does not. In an age of information overload, this tendency is further reinforced as search engines and SNS algorithms prioritize displaying 'information you might like.'

I think the '100 Cognitive Traps Collection' site is like a 'vaccine' against such risks. Just because you know about the existence of biases does not mean you can be completely free from them. However, whether or not you can stop and ask, 'Wait, am I falling into confirmation bias right now?' makes a big difference in the quality of your judgment.

Excellent as a resource for education and training

Another thing I want to emphasize is the 'ease of use as teaching material' of this site.

The 'Let's Think' section for each item includes problems based on classic experiments by Tversky and Kahneman, as well as original tasks, which can be used directly as exercises in classes or training sessions. Have them solve the problem first, then read the 'Explanation.' This order is important; by having them 'experience' how their intuition is betrayed, knowledge transforms into a real-world understanding.

It is perfect for introducing 'biases in clinical reasoning' and 'EBM and critical thinking' in university psychology and behavioral science classes, as well as in medical education. It can also be utilized in corporate training within the contexts of risk communication and diversity. Moreover, since it is free and accessible to anyone on the web, I think there is no reason not to use it.

Conclusion—Let's Become Friends with Bias

Let's summarize what we have discussed so far.

The '100 Cognitive Illusions Collection' is a site with a unique and warm perspective that views cognitive bias not as a 'flaw to be eliminated,' but as a 'partner to understand and live with.' The 100 biases are organized into three categories: 'Memory,' 'Decision Making/Beliefs,' and 'Others/Self.' Each is designed in a four-part structure of 'Catchphrase → Concrete Example → Question → Explanation', allowing you to learn everything from intuition to scientific understanding all at once. Above all, its high practicality as a resource for education and training is its greatest appeal.

We all live with far more than 100 biases. That is natural for a human being; it is nothing to be ashamed of, nor is it something that should be forcibly corrected. What is important is knowing, 'I have this kind of habit, too.' Just knowing that changes how you read the news, how you face patients, and deepens your understanding of yourself.

In the movie 'The Matrix,' the protagonist Neo chooses the 'red pill' and sees the truth of the world. Learning about cognitive bias is a bit like that. It puts a small crack in the comfortable 'world of assumptions.' But what lies beyond that is not anxiety, but a freer and more flexible way of thinking.

You have already made the choice to read this article to the end. With that alone, you have taken the first step toward 're-examining your own thinking.' Please open the '100 Cognitive Illusions Collection' site and go meet the 'inhabitants of assumptions' living inside you. You will surely think, 'Oh, these guys aren't so bad after all.'

My heartfelt thanks to you for reading this far. If you felt it was 'interesting' or 'useful,' it would be a great encouragement if you could quietly press the 'Like' button.

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