UX Laws & Principles
Research-backed UX laws, principles, and methods connected to real insights
Campbell's Law
The more important a metric is in social decision making, the more likely it is to be manipulated. ### Optimisation People tend to optimize their behavior to improve a metric when it's used to determine success or failure, sometimes leading to ridiculous or dangerous results that impact the overall user experience. It's critical that we use data as a tool to assist in decision making instead of allowing metrics alone to determine a decision. ### Limitation Metrics cannot fully and accurately describe the world. Every metric collected reflects a decision about what is considered important. ### Combination The combination of quantitative metrics with qualitative data enables us to better understand the consequences of design decisions. Without this combination, consequences may be missed by relying on passively collected analytics data.
Goal-Gradient Effect
The tendency to approach a goal increases with proximity to the goal. People accelerate their behavior as they get closer to achieving a goal.
Jacob'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.
Pareto Principle
For many events, roughly 80% of the effects come from 20% of the causes. Also known as the 80/20 rule.
Parkinson's Law
Work expands to fill the time available for its completion.
Peak-End Rule
People judge an experience largely based on how they felt at its peak (most intense point) and at its end, rather than the total sum or average of every moment of the experience.
Postel's Law
Be conservative in what you send, be liberal in what you accept. Also known as the Robustness Principle.
Tesler's Law
For any system, there is a certain amount of complexity that cannot be reduced. This complexity must be handled by either the system or the user.
The Principle of Least Effort
People will naturally choose the path of least resistance when completing tasks. Users tend to use the most convenient method available, even if it's not the most efficient.
About UX Laws
UX Laws connect theoretical principles with real research insights. Each law is linked to supporting research findings from usability studies, helping you make evidence-based design decisions.