Many years ago when I worked at Douglas, Long Beach, I wandered the production hangers in my spare time to learn all I could about how their aircraft were built. I forget the exact wording but there were multiple signs that said something like - "Perform the task exactly in accordance with the instructions or cause the instructions to be changed!" That was long before "six sigma" was going to save us all from ourselves.
Maybe Boeing should have saved a few of those signs before they demolished those production buildings.