Thinking Fast and Slow in Design.

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An ex-colleague of mine wrote a post called “Thinking Fast and Slow in Digital”. It was based on the namesake book, Thinking Fast and Slow by Daniel Kahneman. In his post Ronald shared his thoughts on how we can apply the learnings from the book to digital projects.

I’d been meaning to read this book for a while and Ronald’s post prompted me to move it to the top of my list. As I read it I drew my own conclusions about how the psychology described applies to design.

Two modes of thinking.

In the book Kahneman describes humans as having two modes of thinking. He calls them System 1 and System 2. A base understanding of these modes is important for this post.

Thinking fast. System 1 is our automatic instinct. Quick thought based on our model of reality. If a glass smashes nearby you intuitively know roughly where. If I write “box” and “fox” you instinctively know they rhyme. You don’t actively pursue these thoughts, they just happen.

Thinking slow. System 2 is conscious thought. It is rational and intelligible. It questions evidence. It comes to conclusions based on a thorough analysis of the facts available. It is engaged to deal with complex question. Using System 2 takes cognitive effort and tires the brain.

Systems 1 and 2 are both active when we are conscious. System 1 runs automatically and System 2 is in a state of rest most of the time. System 2 is only engaged for deeper thought when System 1 hits a complex problem or finds something which doesn’t match it’s mental model of reality.

Applications in design.

We design digital with users at heart. We aim for the experiences we create to produce good feelings for our users. In his book, Kahneman explores the concept of Cognitive Ease. The ease with which our brain processes information. He describes that when something is easy to process it produces good feelings, it feels effortless. If your user can interact with your products without engaging System 2 too much then they will find it a pleasant experience.

“It appears to be a feature of System 1 that cognitive ease is associated with good feelings.”

On the contrary, if your user is regularly forced to think or surprised by what they see then they will engage System 2 more often. This means they are thinking more and draining their cognitive resources.

I’m sure you’ve experienced landing on a website from Google, taking one look and instantly hitting the back button. It’s less effort to navigate to a different result than it is to try and use a site that appears hard to use.

This should be of great interest to designers who want to create simplicity in the systems they design. Throughout the book Kahneman explores a number of psychological biases and principles all backed by evidence. In this post I’ve picked out some of the key principles I believe we should be aware of whilst designing.

“When something is easy to process it produces good feelings, it feels effortless.”

The halo effect.

The five second test is a popular user research technique to measure impressions. The user is shown a screen for five seconds, then asked for their impressions. The reason this is effective is because it reveals snap judgements and impressions. Shown an app, site or product your System 1 will instantly make a number of judgements without your request.

For each of the screenshots below try to identify the judgements and impressions your System 1 makes without you thinking about it.

Site 1

Site 2

You’ll have spotted they are both bike shops. You may have thought words like dark or light. Busy or minimal. Cheap or expensive. Premium or affordable. You thought all of this as an automatic response.

When a user first see’s your site they will automatically judge it. The halo effect is a cognitive bias whereby the judgement of one aspect of something will affect the overall impression.

Nisbett & Wilson (1977)1 demonstrated this in peoples impressions of others. The appearance, mannerisms and accent of a college instructor were rated as appealing when he acted in a warm manner. With a second group he acted in a cold manner and those same attributes were rated as irritating.

If the initial judgement of your website is negative then the overall impression it leaves will be largely affected by this.

1. The halo effect: Evidence for unconscious alteration of judgments. Nisbett, Richard E.; Wilson, Timothy D. (1977)


Our second concept is Familiarity. The more a user’s previous experiences can help them understand how your site works, the less they have to engage System 2 to understand it. The more familiar they are the less they have to think.

Consider the logo. The expectation is that clicking it will take you to the homepage. If this expected behaviour happens System 1 will happily keeping going without requiring effort from System 2. However, let’s imagine it instead takes you to a product listing page. Now the user is experiencing something unfamiliar and System 2 must be engaged to make sense of it.

Certainly for key functions of the site you should aim to work with design patterns that your audience will be familiar with. This doesn’t have to limit creativity, but you should work to meet expected behaviours and avoid excess cognitive load.

This can of course be turned on its head. If you are designing something thought provoking and you want users to act more slowly and thoughtfully, causing System 2 to engage will achieve this.


Consistency follows naturally from familiarity. When you draw analogies with systems you use everyday it’s clear why consistency is important. Imagine some green lights meaning go and others meaning stop. Or the accelerator in some cars being on the left and others on the right. It would be confusing and irritating. And it would force you think, hard.

System 2 engages when things aren’t as expected so it’s important to be consistent with layout and visual language.


There is a reason most websites have either navigation vertically on the left or horizontally at the top. The same reason is why the hamburger menu has had bad reviews, bad reports and rejection from usability stalwarts. Consistency. Users have grown to expect left vertical or top horizontal navigations. The hamburger disrupts this consistency.

Visual language.

Style guides are in fashion. The United States government use one, so do Mailchimp and of course Google. Why are they so popular and so encouraged? Because they provide consistency. And consistency wins.

Across your site common components like the main navigation, forms and content blocks should be consistent so users can instantly recognise them as they move around your site. The same goes for elements like header levels, links and buttons.


The anchoring bias dictates that in decisions involving numbers our judgement is biased by other information available to us. Remember System 1 is lazy, it doesn’t question or rationalise.

Kahneman explains a study of soup sales in a supermarket. The soup was marked with a discount for a period of two weeks. For a further two weeks the same discount was applied but a sign was also hung stating a maximum of 12 cans per customer. With the sign (and the anchor of 12), customers purchased twice as many cans than without it.

This has applications to encourage favourable product reviews for a product by showing a favourable review near the review submission form. It could encourage higher donations through an online donations page by suggesting a high donation.


Simpler language always wins. It doesn’t matter who your audience is. Judges, teachers, astro-physicists they all prefer simple language. Why? They recognise words instantly, it’s easy to retrieve meaning from memory and takes very little thought to process. System 1 can handle it.

In a previous job I worked at a medical device manufacturer. Product Managers constantly told me that our customers have to be spoken to using medical language or we’ll sound stupid. This is false. In fact this myth was busted by an aptly named study, “Consequences of Erudite Vernacular Utilized Irrespective of Necessity: Problems with Using Long Words Needlessly“. In this study Professor Danny Oppenheimer showed that dressing words up in pretentious language is taken as a sign of poor intelligence and low credibility.

“Simpler language always wins.”

So use simple language when the opportunity allows. Use, don’t utilize. Help, don’t facilitate. Combine, don’t consolidate.

If that isn’t enough to convince you my point is backed by a former President. On October 13th 2010, President Obama signed the Plain Writing Act of 2010. A law that forces communication from the government to be in plain language.

Limit hard thinking.

Limit the amount of hard thinking your user has to do to interact with your product. Help them complete their tasks, find that bit of information they are after or simply to browse. Put the design effort in to make your product familiar, consistent and simple.

As I mentioned at the beginning of this post users will often prefer to put effort into finding a different system than trying to learn one that they perceive as difficult.

If you’re going to take one thing away – keep it simple.