As conversion rate optimization (CRO) experts, we usually test a lot of things on our website, and we’re confident that, by and large, we can get to understand our website visitors, what they like and don’t like, and how to optimize their user journey.

The reality of consumer psychology, however,  means this process is in fact much more complicated than one would think.

Ignoring the true complexity of how consumers make decisions — or, more vastly, how the human brain operates — is to let slip away a wealth of effective website optimization ideas. It also means we remain ignorant as to the real reasons why a website optimization test performed the way it did.

This is the issue that Eline van Baal, Lead Psychologist at Online Dialogue, and Hanneke Gruppo, Country Manager at AB Tasty, explored during this year’s Emerce Retail Europe event in Amsterdam.

Our Dual-Processes Brain

To begin to understand how “the unconscious motivates conversions”, Eline and Hanneke demonstrated that we have to come to terms with a very basic fact:

The conscious “self” that you and I experience as the agents of our lives, is not, in fact, in total control.

Or, in other words, there’s another part of ourselves — the unconscious part — that exerts a powerful and unperceived influence over our conscious thinking, actions and decision-making.

We can refer to these as Systems 1 and 2.

System 1 and System 2


These two systems were explored in groundbreaking research by Dr. Daniel Kahneman. He explains that, in addition to our ‘conscious self,’ (System 2), there is an unconscious part of us, which developed, evolutionarily speaking, long before System 2. Both of these systems affect how we make decisions, including decisions about purchasing, online behavior, how we navigate through a website, etc…


System 1 (Unconscious)System 2 (Conscious)
Thinks “fast”“Slow” thinking
IrrationalThe self we’re familiar with, has ‘agency’

What’s interesting for CRO specialists is that this unconscious System 1 often informs these decisions on a level neither the consumer, nor the CRO specialist designing website optimization campaigns, are aware of!

“System 1 operates automatically and quickly, with little or no effort and no sense of voluntary control. System 2 allocates attention to the effortful mental activities that demand it, including complex computations. The operations of System 2 are often associated with the subjective experience of agency, choice, and concentration.” – Daniel Kahneman, Thinking, Fast and Slow

Cognitive Biases

“System 1 continuously generates suggestions for System 2: impressions, intuitions, intentions, and feelings. If endorsed by System 2, impressions and intuitions turn into beliefs, and impulses turn into voluntary actions […] You generally believe your impressions and act on your desires, and that is fine — usually […] System 1 has biases, however, systematic errors that it is prone to make in specified circumstances.” – Daniel Kahneman, Thinking, Fast and Slow

One of the most flagrant examples of System 1’s influence – and the most useful for CRO professionals – is that of cognitive biases. A cognitive bias is the systematic tendency, used by the brain as an information processing shortcut, to base judgment, memory, decision-making, etc., on one’s personal frame of reference instead of on rational logic. Its an effect of System 1’s unperceived  influence on System 2.

If properly understood, they can also be harnessed to increase online conversion rates. Here are two real-life examples to illustrate:

The Bandwagon Effect

The bandwagon effect is a psychological phenomenon in which people do something primarily because other people are doing it, regardless of their own beliefs, which they may ignore or override. As you might imagine, this cognitive bias is often found operating in the fashion industry (trends, influencers, etc).

The below example shows just how powerful it can by. The ecommerce site BrandAlley added one line to one of their product pages, saying that only a few items were left in stock (implying that the product was very popular). Bypassing logic, or even rational conscious thinking, consumers will tend to see this and “follow the herd”, thinking that they, too, should want the product. Conversion rates went up by 8.8%.


Peak-End Rule Effect

This is the tendency for people judge an experience largely based on how they felt at the highest and lowest point of the experience, rather than on the total sum or average of the experience.  For example, when you’re at the dentist’s, if you spent the better part of an hour in discomfort, but during the last five minutes the discomfort subsided, or on the contrary, if most of the visit was agreeable except for a couple of final, painful minutes, you’re likely to remember each experience as comfortable and painful, respectively.

In the digital word, the most obvious place to exploit this bias is on the checkout page. People often remember if they’ve had a lengthy, complex or terrible checkout experience and often will not complete the purchase, or, they remember how bad their check-out experience was, and won’t return to the website.

For this reason, it’s imperative the check-out process is clear and easy to get through.

One example we’ve worked on is with the fashion company Karen Millen. We worked with them to test different color and copy combinations to help clarify the shopping bag page. We wanted make it more apparent what would happen after clicking on the check out CTA. This clarity and improvement of this page resulted in an increase in clicks of 13% to the CTA.


Gaining an understanding of both systems of cognition (and of course, cognitive biases) is an excellent first step in better understanding your website visitors.  The next step is to test the optimization ideas you have based on this knowledge, to verify which optimization ideas will work best. Running A/B (or multivariate, or multipage…) tests will give you the cold, hard data you need to know how to definitively answer any questions you might have about putting your optimization ideas into practice.