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In his landmark work The Design of Everyday Things, Don Norman synthesized cognitive psychology into six universal design principles governing how humans interact with artifacts:
One of the most consequential conceptual distinctions in modern UI design is the difference between an affordance and a signifier:
When a physical door features a flat pull handle on the push side, users naturally pull—and crash into the door. The handle's physical affordance contradicts its mechanical operation.
In digital software, a 'Norman Door' occurs whenever an interactive element lacks adequate signifiers (e.g., flat, unstyled text that is secretly clickable) or uses deceptive signifiers (styled cards that look clickable but do nothing).
Formulated by psychologist Paul Fitts in 1954, Fitts's Law states that the time required to rapidly move to a target area is a function of the ratio between the distance to the target ($D$) and the width of the target ($W$):
$$MT = a + b \log_2 \left( \frac{2D}{W} \right)$$
Hick's Law (or the Hick-Hyman Law) models human decision-making: the time it takes to make a decision increases logarithmically as the number of choices increases:
$$T = b \log_2(n + 1)$$
When an interface inundates a user with 30 competing links or an unorganized form with 25 visible fields, cognitive load spikes, resulting in decision paralysis or abandonment.
To preserve low cognitive load without stripping advanced capability, designers use progressive disclosure:
Coined by usability authority Jakob Nielsen, Jakob's Law states:
"Users spend most of their time on other sites. This means that users prefer your site to work the same way as all the other sites they already know."
When designers attempt to reinvent ubiquitous interaction conventions (e.g., moving search from the top right/center to a floating widget in the bottom-left corner, or replacing a standard shopping cart icon with a custom proprietary logo), users experience acute cognitive dissonance.
Familiarity reduces cognitive load. Reserve your team's creative innovation for the product's unique core value proposition, not for basic navigation patterns.
In 1956, cognitive psychologist George A. Miller published The Magical Number Seven, Plus or Minus Two, demonstrating that human short-term working memory can hold approximately $7 \pm 2$ discrete chunks of information simultaneously.
In digital design, Miller's Law does not mean interfaces must always feature 7 items. Rather, it mandates chunking: organizing complex data into digestible, semantically coherent clusters:
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