Pareto Principle or 80/20 Rule

The Pareto Principle, or 80/20 rule, suggests that 80% of outcomes come from 20% of causes. For software engineers, it’s a powerful mental model for prioritisation. By identifying the vital 20%, engineers can focus efforts where they yield the highest impact. Prioritising tasks, features, or bugs that offer the greatest value ensures efficient use of time and resources.

One can quickly come up with various adages inspired by the principle:

• 20% of the source code causes 80% of the bugs
• 20% of features deliver 80% of user value
• 20% of customers make up for 80% of sales

Applied thoughtfully, the Pareto Principle can lead to more effective planning and use of time and resources.