Nielsen's 5-User Rule

5 users uncover ~85% of usability issues. More users find the same problems repeatedly.

How to apply it

When you need 'why', talk to 5 people. When you need 'how many', use quantitative.

Practise it on a real challenge

Onboarding — users quit at step 3 and no one knows why

A team wants to know *why* users abandon onboarding step 3.

More UX laws

• 60-30-10 Rule
• 8-pt Spacing Scale
• Accessible contrast
• Aesthetic-Usability Effect
• Alignment Principle
• Calibrated Trust