System 1 and System 2 in testing – part 1

In March 2024 Daniel Kahneman died. He wrote ”Thinking fast and slow”. This book is about how people handle certain situations. He introduced System 1 and System 2.

For the fast observations System 1 is used in most cases. This way of thinking provides fast, almost effortless way to digest information. Like walking to a shop.

For the thoughtful observations System 2 is used. An example is choosing which things to buy in a shop based on a shopping list or availability.

The way users behave, can lead to good test

Supporting System 1


For a test I needed a program. As usually, I went to the system administrator. He gave me some instructions to install the program on my own. I had to change one setting and only needed to press the Next button.

My thought process was like: is this the option? Yes, change it and press the Next button. Otherwise press the Next button. I had the program installed within minutes.

It went so smoothly, because the Next button was on the same place every time.

“The right lower corner of a well designed
the group of a similar looking buttons.
These are a few of my favourite things.”
(On the melody of “My favorite things”)


One of the consequences of the privacy laws is the cookie banner. On one of my favourite web site there are only two buttons: ”Yes, I agree” and “No, thanks” buttons, This is clear and concise.

Knowledge about System 1 in good hands

A good design of the program stimulates the user to use System 1. The program is easy to use.

Abusing System 1


In the past I stumbled on a cookie banner. It had the Accept All button and a More Info button. If I really wanted to visit this web site, then I needed to accept all the cookies. Something I was not looking forward to. It was also not compliant with the privacy laws. There was no way to reject the cookies.

But I was curious, I pressed on the More Info button, A dialog popped up with options to reject cookies. If I only used System 1, then I got unwanted cookies on my PC.


On a cookie banner from another web site, I was looking for a way to avoid unnecessary cookies. In the right lower corner of the dialog there were no buttons. This is my favourite place to look for buttons.

My view went up and I noticed the Accept All button. It had a different background colour than the body of the dialog. I was about to press this button, when I noticed another button to the left.

The Reject all button had the same background as the body of the dialog. It did not get my attention because of the colours of the Accept All button.

This particular button had also a bigger impact on people, who have problems with reading. They might prefer the emphasised Accept All button over the normal Reject All button. Also. people with visual impairment would make the same choice because of the bad contrast.

“The right upper corner of a bad designed
the group of different looking buttons.
These are a few of my dislikeable things.”
(On the melody of “My favorite things”)

Knowledge about System 1 in bad hands

It is possible to make programs in such way that people make bad choices. These situations are called dark patterns. Especially disabled people are easy victims.

“When System 1 rules, when the user clicks,
when the cookies come,
there was nor second thought, nor hesitation,
just a silent urge.”
(On the melody of “My favorite things”)

To be continued.