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title: The Hofstadter’s Law
created: 2024-11-18T09:18:12
modified: 2025-12-30T15:45:43
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In contradiction to [Parkinson’s Law](the-parkinsons-law.md)

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Things usually take longer than you expect, _even when you take into account The Hofstadter’s Law itself_. [^1]

E.g., if you think you’ll finish your homework in an hour, it might actually take two hours.

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# [The Ninety-Ninety Rule](https://en.wikipedia.org/wiki/Ninety%E2%80%93ninety_rule) in Software Engineering

The first 90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent of the code accounts for the other 90 percent of the development time.

[When you have 90 percent of a large project completed, finishing up the final details will take another 90 percent.](https://www.nytimes.com/2022/06/02/opinion/david-brooks-life-hacks.html)

Often, the last 10% of a task takes as much time as the first 90% did.

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# [The Energy-Output Curve](https://www.sahilbloom.com/newsletter/the-energy-output-curve) by Sahil Bloom

The final 5% of the work costs an extra 100%. In other words, it may take 100 units of effort to get to 95% quality, but that final 5% will take another 100.

The final 5% is where good work becomes [great work](do-great-work.md).

Great work isn’t unlocked by wanting greatness more. It’s unlocked by placing an unreasonable amount of care into the craft itself.

The margin between **good** and **great** is narrower than it seems. What begins as a slight edge over the competition [compounds](the-compounding-effect.md) with each additional contest.

![](https://cdn.prod.website-files.com/66915d91469ad34b8324ab88/695184197510a7e65f0a1f73_email.jpeg)

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See also: [The Goal-Gradient Effect](https://sketchplanations.com/goal-gradient-effect)

[^1]: Similar to [The Planning Fallacy](https://en.wikipedia.org/wiki/Planning_fallacy)