https://en.wikipedia.org/wiki/The_Mythical_Man-Month#The_second-system_effect https://en.wikipedia.org/wiki/The_Mythical_Man-Month#The_sec... The authors decid

https://en.wikipedia.org/wiki/The_Mythical_Man-Month#The_second-system_effect https://en.wikipedia.org/wiki/The_Mythical_Man-Month#The_sec... The authors decided to redo the underlying library. And change the user interface. And go cross platform. That amounts to a virtual rewrite from scratch.