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UX principles

Laws of UX

The Laws of UX site is a fantastic resource for learning in depth about mental models, heuristics, and immutable laws of human behavior that undergird the practice of user experience design.

Whereas the Laws of UX site presents in a numerical order, that order is just alphabetical with numbers. For the purpose of this site, the ordered list establishes an opinionated priority, with 1 being more important than 2, and so forth. In the event that two solutions or even their underlyring principles conflict, the answer abiding to the lowest-number law in the list is the one that should be chosen.

  1. Occam’s Razor

    Among competing hypotheses that predict equally well, the one with the fewest assumptions should be selected.

    Especially where users' attention is concerned, less is more. If a single form field can do, don't split it into 3. If a section can be a heading, some text, and a little bit of space, avoid a complex layout. Keep it simple.

  2. Jakob’s Law

    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 you can stick to convention, reuse obvious patterns, and avoid reinventing the wheel, it's better for eveyone to do so.

  3. Fitts’s Law

    The time to acquire a target is a function of the distance to and size of the target.

    Fitts' Law seems underappreciated compared to other interaction guidance. On this site, important interactive elements should always be big and nearby. Any two elements should have adequate spacing to prevent misses.

  4. Law of Proximity

    Objects that are near, or proximate to each other, tend to be grouped together.

    We are strongly inclined to group related content together: at the page and menu level, on a page via sections and the heading outline, and in smaller ways both visually and syntactically.

  5. Serial Position Effect

    Users have a propensity to best remember the first and last items in a series.

    We want the starts and ends of things to be the best parts. People derive value from the middle of a story or a section containing supplementary information, yes, but they retain the headline and the call to action. Prioritize this over Miller's Law, slightly.

  6. Miller’s Law

    The average person can only keep 7 (plus or minus 2) items in their working memory.

    This, coupled with the serial position effect, should be the basis for navigation menus. Each level of menu (with Occam's Razor driving toward a minimal number of levels) should start and end with the most important items, and should number no more than 9 items, ideally 7 or fewer.

  7. Law of Common Region

    Elements tend to be perceived into groups if they are sharing an area with a clearly defined boundary.

    Useful to keep in mind when making a small part of an interface, like a fieldset or layout column. The use of a background, border, or tactical spacing can yield benefits for making an element or elements easier to understand.

  8. Doherty Threshold

    Productivity soars when a computer and its users interact at a pace (<400ms) that ensures that neither has to wait on the other.

    We set a performance budget to ensure that everything on the site is as snappy as can be. Where practical, such as the moodboard and identity documentation, we also specify that transitions and animations remain within the Doherty Threshold.

  9. Postel’s Law

    Be liberal in what you accept, and conservative in what you send.

    It's vitally important, especially in the context of inputs, that we accept user inputs liberally. In the context of Falsehoods programmers believe about names and the CRM/MA convention of splitting name fields, we want to fight back and let users be their authentic selves. And receiving data means respecting users' privacy.

  10. Aesthetic Usability Effect

    Users often perceive aesthetically pleasing design as design that’s more usable.

    This principle is less important in a decision-making framework because aesthetic can derive from simplicity, from convention, and via detail work rather than foundationally. Aesthetic is also more subjective than other laws and effects in this list.

Secondary laws

All laws from the reference site are included, though some are under-emphasized and others deemed redundant or harmful. The remaining laws in the list below should not directly drive decision-making.

  • Pareto Principle

    For many events, roughly 80% of the effects come from 20% of the causes..

    This is a useful mental model and certainly a strong effect. For largely-static sites rather than contributory efforts (such as wikis), though, the 20% of causes is largely known and internal to the brand.

  • Peak-End Rule

    People judge an experience largely based on how they felt at its peak and at its end, rather than the total sum or average of every moment of the experience.

    We want to keep this in mind, especially when telling stories; a good story takes great care to make a satisfying climax and ending. For a website, we have to battle serial position and "the fold" against the peak-end, since bounces can mean very quick starts, peaks, and ends for some user segments. Defer to the serial position effect ten times for every application of the Peak-End rule.

  • Parkinson’s Law

    Any task will inflate until all of the available time is spent.

    Less a driver of decision-making and more a joke about project management... We should aspire to provide maximum value for available time. Perhaps the lesson from this 'law' is to always have an enticing backlog!

  • Von Restorff Effect

    When multiple similar objects are present, the one that differs from the rest is most likely to be remembered.

    Prioritize this effect, wherein a combo-breaker helps drive user engagement (see "Amazon recommends") over implying patterns via the Law of Similarity. At the same time, do not overuse this effect, since it can lead to the "if everything is bold then nothing is bold" feeling.

  • Law of Similarity

    The human eye tends to perceive similar elements in a design as a complete picture, shape, or group, even if those elements are separated.

    An interesting effect, certainly. However, if a design relies on similarity and difference rather than being simply enhanced by the effect, it is a likely sign of too much visual complexity driving the design.

  • Tesler’s Law

    For any system there is a certain amount of complexity which cannot be reduced.

    Yet another corollary of Occam's Razor, albeit insightful. We want to convey meaning to users as simply as possible. Any simpler and the meaning falls apart. Any more complex and the conveyance is inefficient. We want as simple as we can, but no simpler.

  • Law of Uniform Connectedness

    Elements that are visually connected are perceived as more related than elements with no connection.

    Another corollary, this time of the law of proximity. Things that are connected are by definition proximate. Let's Occam this and keep in mind how important proximity is.

  • Law of Prägnanz

    People will perceive and interpret ambiguous or complex images as the simplest form possible, because it is the interpretation that requires the least cognitive effort of us.

    Both a corollary of Occam's Razor and a fairly-minute effect compared to regular-old clear communication. All Gestalt demonstrates that humans recognize and process perceived patterns with innate biases. If an interface relies on Prägnanz in a meaningful way, it's likely too complex of a design to begin with.

  • Zeigarnik Effect

    People remember uncompleted or interrupted tasks better than completed tasks.

    Some psychological principles are true, but not necessarily pleasant. This effect enhances memory while increasing anxiety. We don't want our visitors to feel anxious about completing tasks, and we don't want users to feel like a first-year marketing intern is sending them a "time's running out" email. Just note that this is a tool in the black-hat UX box and move on.

  • Hick’s Law

    The time it takes to make a decision increases with the number and complexity of choices.

    This is a corollary of Occam's Razor; while true, in the interest of abiding by our first principles we'll de-prioritize it.