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How I learned to think fast and slow - the one book that improved my critical thinking

Thought exercise

A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?

Take a minute to think about the answer.

This article is based on my video in developerHabits on the same topic:

My story

I remember being in the army, listening to a presentation about thinking under stress situations. The presenter asked us the bat and ball question and told us to give the answer as quickly as possible. Being a smart guy, I immediately thought "easy, the answer's 10 cents". Well, if you do the maths, you'll understand it's incorrect. And after hearing the correct answer, I understood I'm not that smart.

That seemingly random moment reminded me of many previous situations where I've made bad decisions or given incorrect answers because of rushing and not taking time to think properly. That's when I decided it's time to change something in my thinking. I started researching the topic and often found myself being introduced to the concept of "critical thinking". So what does it mean?

What does critical thinking mean?

Very simply put, critical thinking means analyzing the information you've got in order to form a judgment (a more detailed definition). When we're communicating with others, consuming knowledge from media, researching new tech, etc, we should try to separate opinions and facts. And analyze them. Regarding facts, it's a bit easier - you can check them up. With opinions, it really depends on who's giving an opinion on what. After doing that can you form a more knowledgeable decision. Understandably, it's not feasible to analyze everything all the time. That's why we use heuristics to make our lives easier. But sometimes, using heuristics can also lead us to the wrong conclusions, which we then take as truth.

How to improve your critical thinking?

Me with my copy of the book

As someone relying too much on mental shortcuts and trusting others' opinions too much, I was looking for a way to improve myself. I read tons of articles, watched Youtube videos and even went to coaching, but what really shook my thinking, was a book called "Thinking fast and slow" by Daniel Kahneman. It drastically impacted the way I think and now I'm going to share some of the points I found impactful from the book:

Takeaways from "Thinking Fast And Slow"

System one and system two

"Thinking Fast and Slow" introduces us to two agents of thinking - system one and system two.

System one is fast, not very thoughtful and uses shortcuts. It's usually the agent doing the thinking when you do simple math like 2+2, form first impressions on people you meet and in my case...answer the bat-and-ball question.

System two is analytical and rational. When someone asks you a complex question that makes you think, it's usually system two that does the work. For example - what is 23x43? You probably don't know the answer by heart and need to do some calculations.

System 1 and system 2

That said, both of the systems are needed - when programming complex functions, you most certainly should utilize system two, whereas choosing the next song in your Spotify playlist can be a job left for system one.

Replying to simpler questions

A big chunk of "Thinking fast and slow" is explaining how system one may lead you to unthoughtful decisions because of the shortcuts it uses. One of those shortcuts is answering simpler questions.

If a system one encounters a question that's hard to answer, it'll replace the question with an easier one. For example - "should I invest in that company?" will be replaced with "do I like that company?"


As a developer, I feel bad now. There are many projects I've failed to deliver in time just because I've been over-optimistic. Always thinking that THIS project is different and THIS time we will get things done, although experiences with similar cases have proven otherwise.

For some reason, people are prone to make plans according to the best-case scenarios. They underestimate the costs and overestimate the benefits.

Next time when planning a project, keep that in mind.

Hindsight bias

"Aaah, I knew it will cause an error". Well, why did you deploy it then?

We tend to rebuild our memories and understandings based on past events. And it has a huge role to play in our lives.

"Hindsight bias has pernicious effects on the evaluations of decision-makers. It leads observers to assess the quality of a decision not by whether the process was sound, but by whether its outcome was good or bad… We are prone to blame decision makers for good decisions that worked out badly and to give them too little credit for successful moves that appear obvious only after the fact…" ("Thinking Fast And Slow", Daniel Kahneman, p 203)

Halo effect

Can a doctor recommend you a medicine? Yes, of course. It's a doctor we're talking about. What about a programming language for your next project? Well, the answer depends.

I used to believe people just because they had proven their knowledge in one field. But that doesn't mean they're knowledgeable in some other field.

The Halo effect basically means that our (positive) perception of a person influences how much we believe and trust them. And well...doctors must be smart, but they may not always know about programming languages.

WYSIATI: What you see is all there is.

This bias means that you form your opinion only based on the data you've got. And system one is really quick to form beliefs on that information.

As a critical thinker one should know that in most cases, there's more information out there, more to analyze. Of course, sometimes there's no access to different kinds of sources and that's when you should acknowledge that your conclusion is just based on the information at hand.

So next time, when making decisions, try to gather information from various sources and analyze different possibilities.

Sunk-cost fallacy

Probably many of us have been in a situation where we continue building a poor system just because we've invested too many resources, know in our hearts it's about to fail. Well...that's what sunk-cost-fallacy is all about. Simply put, it's our inability to realistically assess other options(that may bring higher returns) when we've invested enough of our resources.

My English vocabulary isn't rich enough to express the emotions I felt and the thoughts I had after finishing "Thinking Fast and Slow". What I can say is that it had a huge impact on the way I think and it definitely made me a better developer, a better person. I've gotten better in differentiating opinions from facts, analyzing media and filtering what I say, think. There's room to grow though.

I'm not saying that one must be analytical and thoughtful all the time, but at least in our professional environment, one should implement critical thinking in order to make better decisions. In my case, reading "Thinking fast and slow" was a huge step towards that.

If growth-mindset and developer lifestyle is something you're interested in, then please do follow developerHabits in Youtube and Instagram.

Also, make sure to get yourself a copy of "Thinking Fast and Slow" from Amazon(includes my affiliate).

Top comments (2)

brettimus profile image

this is one of those articles that I read and I'm shocked it doesn't have more <3 and unicorns and stuff on it! well written, and helpful. I've had that book on my list for years. I'm glad someone else read it! hahah

kethmars profile image

Wow. Thank you for your kind words, I genuinely appreciate it!
Regarding the book - do it :D! It's truly worth the time and effort.