Galls Law
A complex system that works is invariably found to have evolved from a simple system that worked. A complex system designed from scratch never works and cannot be patched up to make it work. You have to start over with a working simple system.
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Origin
John Gall (1925–2014), a pediatrician who trained at the Mayo Clinic and practiced at the University of Michigan, formulated his law in General Systemantics, first published in 1975 as a wry critique of systems theory. A third edition, retitled The Systems Bible, appeared in 2002. Never presented as formal research, Gall distilled it from observation — an aphorism that spread widely in software engineering long after the book's quiet debut.
Updated February 22, 2026