the ninety-ninety rule
expressionprogrammingops culture
'The first 90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent accounts for the other 90 percent.'
Tom Cargill of Bell Labs coined it and Jon Bentley's 1985 Programming Pearls column made it canon; the arithmetic is the joke and the truth. Demos, happy paths, and prototypes are the first 90; edge cases, integration, and polish are the second. Every 'almost done' status report is the rule mid-execution.