Pareto Principle (80/20 Rule)
Why 80% of outcomes come from 20% of inputs—and how to leverage this for massive productivity gains.
Tiny Summary
The Pareto Principle states that roughly 80% of effects come from 20% of causes. In software: 80% of bugs from 20% of modules, 80% of value from 20% of features, 80% of usage from 20% of users.
The Pattern
┌────────────────────────────────────────┐
│ ################## (20% of causes) │ → 80% of effects
│ #################### (80% of causes) │ → 20% of effects
└────────────────────────────────────────┘
Software Applications
Features: 20% of features deliver 80% of user value → Build high-impact features first
Bugs: 20% of modules cause 80% of crashes → Fix critical modules first for massive stability gains
Performance: 20% of code paths consume 80% of CPU/memory → Profile first, optimize hot paths only
Customers: 20% of customers generate 80% of revenue → Optimize for power users
Code Changes: 20% of changes cause 80% of production issues → Add extra testing to high-risk areas
How to Apply
1. Measure: Use analytics to identify the vital 20% (feature usage, bug frequency, performance profiles)
2. Prioritize: Focus resources on high-impact work (schedule critical features, assign best engineers to hot paths)
3. Ignore strategically: Low-usage features can have bugs, edge cases don't need perfect UX, technical debt in unused code can wait
Quick Scenarios
Sprint Planning: 10 feature requests → Build top 2 → 80% of value delivered
Bug Triage: 100 bugs → Fix top 20 by frequency → 80% of crashes eliminated
Refactoring: 50 files → Profile → Optimize 10 hot paths → 80% speedup
Key Insights
Don't guess which 20% matters—measure it with data. Focus energy where it compounds. Accept that the 80% doesn't need to be perfect. The vital 20% changes over time, so keep measuring.
Use the simulation to experiment with different impact distributions!