Gall's law
expressionprogrammingops culture
A complex system that works is invariably found to have evolved from a simple system that worked.
John Gall wrote it in Systemantics (1975), with the sharper converse: a complex system designed from scratch never works and cannot be patched into working; you must restart from a working simple system. It is the theoretical backbone of iterative delivery, MVPs, and the strangler-fig pattern for rewrites. Big-bang redesigns fail on schedule; Gall explained why in advance.