Lean thinking teaches reasoning, not rules
What are the rules for using “Red Bins”? It depends. What is the rule for stop-at-every-defect? I don’t know, it depends. What are the rules for effective problem solving? Let me see… it depends.
People want rules to get on with their work and not have to think things through too much, which is understandable. Bosses want rules to, well, rule. Organizations want rules because without rules (and roles) where would we be?
Lean thinking doesn’t teach rules because no two situations are the same: it teaches you a way of thinking, typical reasoning.
For instance I have no idea whether we should stop work at every doubtful part, obvious defect, five defects or whatever. What I do know if that if we put aside defective work to continue to produce in order to achieve the output no matter what, the defectives put aside take precious place, require resources to handle, and the longer we wait between investigation (if we have a stock of defectives to check there will be a queue) the farther we’ll be from the context of the problem, so the smaller the chances of catching the cause of the problem. This will lead us to accept that the process works normally, with a certain percentage of random defects, which adds considerable cost to every product in the end.
On the other hand, stopping right away when something is not right means feeling the tension to keep up with takt time, means investigating right away all the Manpower, Machine, Material, Methods standards of how the work is done, and probably means learning something on the spot that will lead to improving the process and peeling one further layer of waste of the process thus lowering overall cost.
The lean tools themselves support a certain kind of reasoning, nothing more. The way you design the tool, orients what typical reasoning you expect people to make. The tools, really, really matter, not for compliance, but for support to thinking.
So yes, it depends – not two situations are alike. And yes the same typical reasoning, (such as reduce batch size to improve on time delivery, or create continuous flow to improve productivity) applies time and time again in all sorts of situations, but not “as a rule”, as a way of thinking of what is going on and of discovering how overburden and unlevelness lead to waste – and unnecessary costs to customers, people and the business as a whole.
The point of rules is to stop you from thinking: just follow the rule! Lean is about making you think, and think!
