In writing life critical systems like the Space Shuttle's operating system, effectively 99.9% of all work is QA.

MS had the dominant operating system in the world, and keeping its userbase and its ~monopoly dividend would have been more profitable as a business than doing... everything it's done in the past twenty years. Selling software that all the people use all the time just has a lot less opportunity for growth than making new software, according to Investor Brain.