15 laws · 378 terms
From cognitive biases to visual design — understand the psychology, methods, and frameworks that shape every interface.
Chapter 1
3 laws
Decision time increases logarithmically with the number of choices.
Hick's Law (or the Hick-Hyman Law) describes the time it takes for a person to make a decision as a function of the number of possible choices. The more choices, the longer the decision takes — the relationship is logarithmic.
Choose the number of options to test:
Time to reach a target depends on distance and size.
Fitts's Law predicts that the time required to rapidly move to a target area is a function of the ratio between the distance to the target and the width of the target. Larger, closer targets are faster to click.
Users spend most of their time on other sites and prefer yours to work the same way.
Jakob's Law states that users spend most of their time on other websites. This means they prefer your site to work the same way as all the other sites they already know. Users transfer expectations from familiar sites to new ones.
Task: Add an item to your cart in two different store layouts. We'll time you.
Chapter 2
5 laws
The average person can hold 7 (±2) items in working memory.
Miller's Law states that the average person can only keep about 7 (plus or minus 2) items in their working memory at a time. George Miller's 1956 paper 'The Magical Number Seven' established this as one of the most cited findings in psychology.
How many items can you remember? Pick a count:
Users perceive aesthetically pleasing designs as more usable.
The aesthetic-usability effect describes a phenomenon where users perceive more aesthetically pleasing designs as easier to use than less aesthetically pleasing ones — regardless of actual usability.
Form A — Rate perceived ease of use
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How easy does this form look to use?
1 = hard, 5 = very easy
People judge experiences by their peak and end moments, not averages.
The Peak-End Rule states that people judge an experience based primarily on how they felt at its most intense point (the peak) and at its end, rather than based on the average of every moment. Duration of the experience has surprisingly little impact.
Configure the peak moment and ending quality, then experience the sequence.
Peak (step 2)
Ending (step 4)
Items at the beginning and end of a list are remembered best, while middle items are forgotten.
The Serial Position Effect describes the tendency for people to recall the first and last items in a list far better than the middle items. This phenomenon was first identified by Hermann Ebbinghaus in the 1880s through his pioneering memory experiments.
You'll see 10 words, one at a time. Then try to remember as many as you can.
Items that stand out from their peers are more likely to be remembered.
The Von Restorff Effect (also called the Isolation Effect) predicts that when multiple similar items are presented, the one that differs from the rest is most likely to be remembered. Named after psychiatrist Hedwig von Restorff who first documented it in 1933.
A grid of items will appear. Click the one that stands out as fast as you can.
Chapter 3
4 laws
People perceive complex shapes as the simplest form possible.
The Law of Prägnanz (also known as the Law of Good Figure or Law of Simplicity) states that people will perceive and interpret ambiguous or complex images as the simplest form possible. Our brains prefer order, symmetry, and simplicity.
Toggle between complex and simplified forms:
Elements close together are perceived as related.
The Law of Proximity states that objects near each other tend to be perceived as a group. This Gestalt principle is one of the most fundamental tools in visual design — spacing communicates relationships.
Adjust spacing to see how proximity changes perceived grouping:
Elements feel like 3 distinct groups of 3.
Similar-looking elements are perceived as related.
The Law of Similarity states that elements that share visual characteristics — such as color, shape, size, or orientation — are perceived as being related or belonging to the same group, even when they're not close together.
Change the similarity property to see grouping shift:
Elements in the same bounded area are perceived as grouped.
The Law of Common Region states that elements tend to be perceived as grouped together if they are within the same bounded region. This is one of the Gestalt principles of perception and is incredibly useful in interface design.
How many groups do you see?
Nine toggles, equal spacing. Proximity alone says nothing about which belong together.
Chapter 4
3 laws
Productivity soars when response times are under 400ms.
The Doherty Threshold states that productivity soars when a computer and its users interact at a pace that ensures neither has to wait on the other. Research by Walter Doherty and Ahrvind Thadani found that system response times under 400 milliseconds are crucial.
Click each button and feel the difference in response time:
Every application has an inherent amount of complexity that cannot be removed.
Tesler's Law (also known as the Law of Conservation of Complexity) states that every application has an inherent amount of irreducible complexity. The only question is who deals with it — the user or the developer.
Drag the slider to shift complexity between user and system. The total complexity stays the same — only who handles it changes.
The simplest solution is usually the best.
Occam's Razor (or the law of parsimony) states that among competing hypotheses, the one with the fewest assumptions should be selected. In design, this translates to: the simplest solution that solves the problem is usually the best one.
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