80-20 Rule

For archive (Updated on February 18, 2019)


The 80-20 Rule is also known as Paretto’s Principle.

The rule was based on the observation of land ownership.
e.g. 80 per cent of the land is owned by 20 percent of the population.


  • The rule has been extended to other realms and applications. e.g. 80 per cent of one’s time is often spent in doing 20 percent of the tasks.
  • The numbers do not have to be exact. One version is the 70-30 rule by Professor Donald Knuth. He found out that 70 per cent of the computing time was spent in 30 per cent of the code.
  • The numbers need not add up to 100. The essence of the rule is “Not all tasks are equally important.” If one has limited resources, one should prioritize the tasks to be executed and/or improved.

U Khin Maung Zaw (KMZ, EC76) added :

Some 10/15 years ago, before the advent of Cloud among others, we described the new versions of software products, Microsoft Windows and Office included, as 80/20. It was the outsiders’ view in those days as 80% of the features were being used by 20% of the users, the remaining 20% being used by majority 80% of the users. At some point some users raised it to 90/10, as more and more features were added, and many day-to-day users seemed oblivious to the added features.

[This is not necessarily software products like Windows/Office products, but many others in our daily life.]

In another scenario, as U Hla Min alluded above, the majority of the code paths in a given software package are not executed in normal scenario. The developer has to add a lot of code paths to perform tasks.

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