Extreme Users Principle

Users at the extremes of familiarity or ability often highlight design issues that moderate users experience less acutely.

Someone completely unfamiliar with a product encounters friction that experts have learned to work around. Someone with expertise notices limitations invisible to casual users. Someone with accessibility needs reveals assumptions baked into the design.

The principle applies bidirectionally: interview both people extremely familiar with the product and people completely unfamiliar. Each extreme illuminates different blind spots in the design.

This isn’t about designing only for extremes, it’s about using extremes as a lens to see problems that affect everyone but remain invisible in average-case research.

Related: 01-atom—say-do-gap