UX Design Principles Skill

Psychological principles that guide design DECISIONS. For implementation patterns (colors, spacing, animations), see the corresponding ux-* skills.

Choice Architecture

Hick's Law: Decision Time

Decision time increases with the number and complexity of choices.

Do:

• Reduce options when quick decisions matter
• Break complex tasks into smaller steps
• Highlight recommended or default options
• Use progressive disclosure for advanced features

Don't:

• Present all options at once without guidance
• Oversimplify until purpose becomes unclear

Choice Overload

Too many choices overwhelm and paralyze.

Do:

• Limit options when quick decisions are important
• Provide comparison tools (e.g., side-by-side pricing)
• Prioritize content and offer filters to narrow choices

Don't:

• Present all possible options at once
• Force users through large unfiltered selection lists

Serial Position Effect

Items at the beginning and end of lists are remembered best.

Do:

• Place critical actions at the start or end of navigation
• Put key information first and last in lists

Don't:

• Bury important actions in the middle of menus
• Give equal prominence to all items

Cognitive Load

Cognitive Load Principle

Reduce information users must hold in working memory.

Do:

• Remove distracting elements that don't help task completion
• Distinguish essential information from nice-to-have
• Break complex information into digestible chunks

Don't:

• Present excessive details or decorative clutter
• Mix intrinsic complexity with unnecessary extraneous load

Implementation: See ux-spacing-layout for visual chunking patterns.

Law of Pragnanz (Simplicity)

People interpret complex images in the simplest form possible.

Do:

• Present information in simple, ordered forms
• Reduce visual complexity to aid comprehension

Don't:

• Overwhelm users with ambiguous or complex graphics
• Create layouts that require mental effort to parse

Tesler's Law (Conservation of Complexity)

Every process has irreducible complexity that must be handled somewhere.

Do:

• Handle inherent complexity in design/development, not on users
• Provide context-aware guidance within the interface
• Accept that users are not always rational

Don't:

• Push system complexity onto users
• Build only for idealized, rational behavior

Occam's Razor

Simplest solution is usually best.

Do:

• Eliminate unnecessary elements while maintaining function
• Continually refine until nothing can be removed without harm

Don't:

• Add features that complicate without clear user benefit
• Solve simple problems with elaborate solutions

Attention & Perception

Selective Attention

Users naturally filter out irrelevant content.

Do:

• Guide attention to relevant information
• Minimize distractions
• Ensure only one significant change occurs at a time

Don't:

• Style important content like advertisements (banner blindness)
• Introduce multiple simultaneous changes without cues
• Place essential info in areas typically ignored (ad zones)

Von Restorff Effect (Isolation)

Distinctive items are remembered better.

Do:

• Make important actions visually stand out
• Use emphasis sparingly so items don't compete
• Provide multiple contrast cues (shape, pattern, not just color)

Don't:

• Rely exclusively on color to convey importance
• Overuse emphasis (dilutes impact)
• Use motion effects that trigger discomfort

Implementation: See ux-color-system for emphasis patterns.

User Expectations

Jakob's Law

Users transfer expectations from familiar products.

Do:

• Design consistent with patterns users already know
• Leverage existing mental models
• When making major changes, offer temporary familiar alternatives

Don't:

• Radically alter established interactions without guidance
• Force users to relearn common patterns

Paradox of the Active User

Users jump into products without reading instructions.

Do:

• Expect users to start using immediately
• Provide contextual help, tooltips, and guidance in-place

Don't:

• Force users to read manuals before using
• Hide help or make it difficult to find

Aesthetic-Usability Effect

Beautiful design is perceived as more usable.

Do:

• Design interfaces that look appealing and polished
• Use aesthetics to create positive first impressions

Don't:

• Rely on visual polish to hide fundamental usability problems
• Assume beauty compensates for broken functionality

Progress & Motivation

Goal-Gradient Effect

People work faster as they sense completion is near.

Do:

• Display progress toward goals
• Provide "artificial progress" (e.g., start at 10% complete)

Don't:

• Leave users unsure how far they've progressed
• Hide progress information

Implementation: See ux-feedback-patterns for progress indicator patterns.

Zeigarnik Effect

Incomplete tasks stay in memory and motivate continuation.

Do:

• Clearly signify that more content/steps are available
• Provide artificial progress toward goals
• Show progress indicators

Don't:

• Leave tasks without visible progress indicators
• Hide future steps or content

Implementation: See ux-feedback-patterns for progress patterns.

Parkinson's Law

Tasks expand to fill available time.

Do:

• Set clear, reasonable time expectations
• Reduce task duration below what users expect
• Use time-saving features (autofill, shortcuts)

Don't:

• Allow simple processes to take longer than necessary
• Present long forms without automation

Implementation: See ux-form-design for autofill patterns.

Experience Design

Peak-End Rule

Experiences are judged by peak moments and endings.

Do:

• Design memorable peaks and strong endings
• Identify when your product is most helpful and add delight
• Minimize negative peaks (bad moments are remembered vividly)

Don't:

• Neglect the conclusion of user journeys
• Leave negative events unaddressed

Pareto Principle (80/20)

A small number of causes produce majority of outcomes.

Do:

• Identify and focus on high-impact areas
• Allocate resources where they benefit most users

Don't:

• Distribute efforts evenly across all tasks
• Over-invest in low-impact areas

Input & Error Handling

Postel's Law (Robustness)

Be tolerant of input, strict in output.

Do:

• Anticipate various user inputs and behaviors
• Translate diverse input to meet system requirements
• Provide clear feedback for edge cases

Don't:

• Rigidly enforce narrow input formats
• Send malformed or ambiguous output

Implementation: See ux-form-design for validation patterns.

Cognitive Bias Awareness

Cognitive Bias Principle

Mental shortcuts influence decision making.

Do:

• Recognize that heuristics save mental effort but can skew judgment
• Raise awareness of your own biases during design
• Challenge assumptions with your team

Don't:

• Ignore biases like confirmation bias
• Seek only information supporting preconceived beliefs

Quick Reference Matrix

Situation	Apply
Too many options	Hick's Law, Choice Overload
Complex task	Tesler's Law, Cognitive Load
Users skip instructions	Paradox of Active User
Low completion rates	Goal-Gradient, Zeigarnik
Poor first impressions	Aesthetic-Usability
Users confused by changes	Jakob's Law
Important items ignored	Serial Position, Selective Attention
Long task times	Parkinson's Law
Poor memories of experience	Peak-End Rule
Resource allocation	Pareto Principle
Input validation issues	Postel's Law
Overly complex design	Occam's Razor, Pragnanz

Related Skills

• ux-spacing-layout: Visual chunking, grouping (Law of Proximity/Common Region)
• ux-color-system: Emphasis, similarity (Von Restorff, Law of Similarity)
• ux-animation-motion: Response timing (Doherty Threshold)
• ux-accessibility: Touch targets, focus (Fitts's Law)
• ux-feedback-patterns: Progress, loading states (Working Memory)
• ux-user-flow: Navigation, mental models (Flow)
• ux-form-design: Input tolerance, validation (Postel's Law)