Laws of UX: 27 Psychology Principles Every Startup Founder Needs to Build Better Products (2025)
The Psychology Behind Products People Love
Great products aren't just well-engineered — they're designed around how humans actually think, decide, and behave. Jon Yablonski compiled the most important psychological principles for designers into Laws of UX, a collection that has become essential reading for product teams worldwide.
For startup founders, understanding these laws isn't academic — it's the difference between a product that feels intuitive and one that users abandon after 30 seconds. Here are the 27 principles that matter most, organized by how they apply to building your product.
Decision & Choice
How users make decisions — and how your design can help or hinder them.
Hick's Law
The time it takes to make a decision increases with the number and complexity of choices.
For founders: Every additional option in your pricing page, onboarding flow, or feature menu increases decision time — and increases the chance users choose nothing. Reduce choices to the essentials. Stripe's pricing page is a masterclass: one plan, one price, one button.
Choice Overload
People get overwhelmed when presented with too many options — also known as the paradox of choice.
For founders: If your settings page has 40 toggles, users won't configure any of them. Progressive disclosure — showing options only when relevant — keeps users moving forward instead of freezing.
Occam's Razor
Among competing hypotheses that predict equally well, the one with the fewest assumptions should be selected.
For founders: When two design approaches achieve the same goal, choose the simpler one. Complexity is a tax on every user, every day. The simplest explanation of your product should also be the most accurate.
Memory & Cognition
How users process, store, and recall information — and the limits of human attention.
Miller's Law
The average person can only keep 7 (plus or minus 2) items in their working memory.
For founders: Your navigation shouldn't have 12 items. Your onboarding shouldn't ask users to remember 10 steps. Group information into chunks of 5-9 items maximum. Phone numbers are chunked (555-867-5309) for exactly this reason.
Chunking
Individual pieces of information are broken down and grouped together in a meaningful whole.
For founders: Break complex forms into multi-step wizards. Group related settings together. Present data in meaningful clusters rather than endless lists. Notion does this brilliantly with its block-based structure.
Working Memory
A cognitive system that temporarily holds and manipulates information needed to complete tasks.
For founders: Don't make users hold information from one screen to use on another. If step 3 of your flow requires info from step 1, show it. Auto-fill, inline previews, and persistent context reduce working memory load.
Cognitive Load
The amount of mental resources needed to understand and interact with an interface.
For founders: Every element on screen costs cognitive energy. Unnecessary animations, decorative elements, and redundant copy all tax your user's brain. The best products feel effortless because they minimize cognitive load at every step.
Cognitive Bias
Systematic errors in thinking that influence our perception and decision-making.
For founders: You are biased about your own product. Confirmation bias makes you see validation where there is none. Anchoring bias affects your pricing. Survivorship bias skews your customer research. Awareness of these biases is the first step to building for real user needs.
Selective Attention
The process of focusing attention on a subset of stimuli — usually those related to our goals.
For founders: Users don't read your page — they scan for what's relevant to their goal. Design for scanning: clear headings, visual hierarchy, prominent CTAs. Everything else is noise they'll filter out.
Mental Model
A compressed model based on what we think we know about a system and how it works.
For founders: Users come to your product with mental models from other products. If your "save" button doesn't look like a save button, users won't find it. Match existing mental models unless you have an extremely compelling reason to break them.
Familiarity & Expectations
Why users expect your product to work like products they already know.
Jakob's Law
Users spend most of their time on other sites. They prefer your site to work the same way as the sites they already know.
For founders: This is perhaps the most important law for startups. Don't reinvent navigation, checkout flows, or login screens. Users have built expectations from using hundreds of other products. Meet those expectations — then innovate where it matters for your unique value proposition.
Paradox of the Active User
Users never read manuals but start using the software immediately.
For founders: Nobody will read your documentation, help pages, or onboarding tooltips — at least not before trying to use the product. Design your product to be discoverable through use. If users need a manual, your UX has failed.
Postel's Law
Be liberal in what you accept, and conservative in what you send.
For founders: Accept user input in any reasonable format (dates, phone numbers, addresses). Don't reject "555 867 5309" because you wanted "555-867-5309." Be strict in your output — display data consistently. Flexibility in, precision out.
Visual Perception & Grouping
How users perceive visual relationships between elements — the Gestalt principles.
14. Law of Proximity
Objects near each other tend to be grouped together.
Apply it: Place related form fields close together. Separate unrelated sections with whitespace. Users will assume items near each other are related.
15. Law of Similarity
Similar elements are perceived as a complete picture or group.
Apply it: Make all clickable elements look similar (same color, same style). If two buttons look different, users assume they do different things.
16. Law of Common Region
Elements sharing an area with a clearly defined boundary are perceived as a group.
Apply it: Use cards, borders, and backgrounds to group related content. A card around a pricing tier makes all its features feel like they belong together.
17. Law of Uniform Connectedness
Visually connected elements are perceived as more related.
Apply it: Use lines, arrows, or color to show relationships. Progress bars, breadcrumbs, and flow diagrams all leverage this principle.
18. Law of Pragnanz
People interpret complex images in their simplest form — the interpretation requiring the least cognitive effort.
Apply it: Use simple, clean shapes for icons and UI elements. Avoid visual complexity that forces users to "decode" your interface. Simple shapes are processed faster.
Engagement & Motivation
What keeps users engaged — and what makes them come back.
Zeigarnik Effect
People remember uncompleted tasks better than completed ones.
For founders: This is why LinkedIn's profile completion bar works so well. Show users what's incomplete — incomplete profiles, unfinished onboarding steps, partial setups. The brain nags them to finish. Use progress indicators strategically.
Goal-Gradient Effect
The tendency to approach a goal increases with proximity to the goal.
For founders: Users work harder when they feel close to finishing. Start your progress bars at 20% instead of 0%. Coffee shop loyalty cards pre-stamped with 2 of 10 stamps outperform blank cards of 8 stamps — same gap, different psychology.
Flow
The mental state where someone is fully immersed in energized focus, involvement, and enjoyment.
For founders: Flow states happen when the challenge matches the user's skill level. Too hard → frustration. Too easy → boredom. Great onboarding gradually increases complexity. Figma, Notion, and video games all do this brilliantly.
Peak-End Rule
People judge an experience based on how they felt at its peak and at its end, not the average of every moment.
For founders: Nail two moments: the peak (the "aha moment" when users first experience your core value) and the end (confirmation screens, success states, thank-you pages). A delightful checkout confirmation can redeem a mediocre browsing experience.
Attention & Recall
What users notice and remember about your product.
Von Restorff Effect (Isolation Effect)
When multiple similar objects are present, the one that differs from the rest is most likely to be remembered.
For founders: This is why the "recommended" pricing tier is highlighted in a different color. Make your primary CTA visually distinct from everything else. The element that stands out is the one users act on.
Serial Position Effect
Users best remember the first and last items in a series.
For founders: Put your most important navigation items first and last. In mobile apps, the leftmost and rightmost tab bar items get the most attention. In lists, the first and last items are recalled most — bury the least important items in the middle.
Performance & Interaction
How speed and physical design affect the user experience.
Doherty Threshold
Productivity soars when computer and user interact at a pace under 400ms — ensuring neither has to wait on the other.
For founders: If your app takes more than 400ms to respond to user actions, you're breaking flow. Optimistic updates, skeleton screens, and instant feedback (even before the server responds) keep the interaction feeling seamless. Speed isn't a feature — it's a prerequisite.
Fitts's Law
The time to acquire a target is a function of the distance to and size of the target.
For founders: Make important buttons big and easy to reach. On mobile, primary actions should be in the thumb zone. Don't put your CTA in a tiny corner — the bigger and closer the target, the faster users can click it.
Complexity & Efficiency
27. Tesler's Law (Conservation of Complexity)
For any system, there is a certain amount of complexity that cannot be reduced.
Apply it: Some complexity is inherent. The question is: who bears it — the user or the system? Great products absorb complexity internally so the user experience remains simple. Stripe handles payment regulations behind the scenes so developers don't have to.
Pareto Principle (80/20)
Roughly 80% of effects come from 20% of causes.
Apply it: 80% of your users use 20% of your features. Find that 20% and make it exceptional. The rest can be hidden, simplified, or removed entirely. Feature creep is the enemy of great UX.
Parkinson's Law
Any task will inflate until all available time is spent.
Apply it: Set reasonable constraints on user actions. Time-limited offers, character limits, and deadlines prevent decision paralysis. Short forms get more completions than long forms — less space, less inflation.
Aesthetic-Usability Effect
Users perceive aesthetically pleasing design as more usable.
Apply it: Beautiful products get more patience. Users forgive minor usability issues in well-designed products. Invest in visual polish — it's not superficial, it directly affects perceived usability and trust.
The Meta-Principle
All 27 laws reduce to one insight: design for the brain you have, not the brain you wish users had. Humans are impatient, forgetful, easily overwhelmed, and driven by emotion. The best products don't fight human nature — they work with it.
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