Not just variance but also the concept of essential complexity: One cannot possibly hope to control all the variables, and so one must strive to continually see

Not just variance but also the concept of essential complexity: One cannot possibly hope to control all the variables, and so one must strive to continually seek to improve the system ("monitoring/alerting") as defects emerge ("hidden factories"), conduct experiments to evaluate predictions against actual outcomes ("a/b tests"), to not erroneously change systems and processes to fix "special-causes" [but understand that most causes of quality degradation are "commons-causes", which has to be fixed by changing systems and processes ("root-cause analysis")], to not drive down costs for the sake of it but rather seek to drive down long-term costs ("ecosystem"), to have a more humanist approach to management... among a host of other concepts. If you are curious (and have the stomach for some MBA-ness), this article (four parts) should be well worth your time: https://archive.is/tXJhw https://archive.is/tXJhw