galls-lawlisted

# Gall's Law > "A complex system that works has evolved from a simple system that worked. A complex system built from scratch won't work." > — John Gall, 1975 ## The core idea You cannot design a working complex system directly. Complex systems that actually work all share the same history: they started as simple systems that worked, and grew from there. Every attempt to build the final, complete, sophisticated system from the start will fail — or produce something that doesn't actually work in production. This isn't a counsel of despair. It's a guide to how to succeed: **start simple, ship, learn, and evolve.** ## Why complex systems fail when built from scratch - **Unknown unknowns**: You don't know all the requirements until you've operated a simpler version. - **Emergent complexity**: Real-world usage surfaces edge cases, failure modes, and interaction effects that no design can anticipate in advance. - **Integration risk**: Each new component multiplies integration complexity. Building many components at once means many things to go wrong before you have any working baseline. - **Feedback starvation**: Complex systems take longer to build, so you go longer without the real-world feedback that shapes good design. ## The rewrite trap This law is most important when teams want to do a "big rewrite." The existing system feels painful, messy, and unmaintainable. The natural impulse is: throw it away and build the right thing. But the existing system, however ugly, en