Ninety–ninety rule

The Ninety-Ninety Rule is a humorous adage in software development and project management that suggests that "the first 90% of a project takes 90% of the time, and the last 10% takes another 90% of the time." This saying highlights the common phenomenon where initial stages of a project may seem to progress quickly, but the final stages often take significantly longer due to unforeseen challenges, complexities, or the need for refinements and testing.