Why We Miss What's Right in Front of Us

Bug Blindness

Insights from Dan Luu's Research

Based on Hacker News Discussion

02

Understanding Bug Blindness

A cognitive phenomenon affecting developers and users alike

We see what we expect to see,
not what's actually there.

This is the essence of bug blindness.

The Cognitive Reality of Software Development

235

Hacker News Points — A Viral Discussion on Bug Blindness

Dan Luu's research sparked widespread recognition of this phenomenon

05

Why bugs persist and how to catch them

visibility_off

Repeated exposure makes us stop seeing errors we've seen before

psychology

We look for evidence that confirms our expectations, not what contradicts them

speed

Pressure to ship quickly reduces thoroughness in review

auto_fix_high

We trust tools too much and skip manual verification

01

Fresh Eyes Review Have someone unfamiliar with the code review it — they'll spot what you miss
02

Deliberate Negative Testing Actively look for what shouldn't work, not just what should
03

Slow Down Take time to read code carefully, not just skim for patterns
04

Question Assumptions Challenge your expectations about how things should behave

The key to catching bugs is to look for what shouldn't be there — not just what should