The Lean Startup - Eric Ries [81]
In traditional mass production, the way to avoid stockouts—not having the product the customer wants—is to keep a large inventory of spares just in case. It may be that the blue 2011 Camry bumper is quite popular, but what about last year’s model or the model from five years ago? The more inventory you keep, the greater the likelihood you will have the right product in stock for every customer. But large inventories are expensive because they have to be transported, stored, and tracked. What if the 2011 bumper turns out to have a defect? All the spares in all the warehouses instantly become waste.
Lean production solves the problem of stockouts with a technique called pull. When you bring a car into the dealership for repair, one blue 2011 Camry bumper gets used. This creates a “hole” in the dealer’s inventory, which automatically causes a signal to be sent to a local restocking facility called the Toyota Parts Distribution Center (PDC). The PDC sends the dealer a new bumper, which creates another hole in inventory. This sends a similar signal to a regional warehouse called the Toyota Parts Redistribution Center (PRC), where all parts suppliers ship their products. That warehouse signals the factory where the bumpers are made to produce one more bumper, which is manufactured and shipped to the PRC.
The ideal goal is to achieve small batches all the way down to single-piece flow along the entire supply chain. Each step in the line pulls the parts it needs from the previous step. This is the famous Toyota just-in-time production method.8
When companies switch to this kind of production, their warehouses immediately shrink, as the amount of just-in-case inventory [called work-in-progress (WIP) inventory] is reduced dramatically. This almost magical shrinkage of WIP is where lean manufacturing gets its name. It’s as if the whole supply chain suddenly went on a diet.
Startups struggle to see their work-in-progress inventory. When factories have excess WIP, it literally piles up on the factory floor. Because most startup work is intangible, it’s not nearly as visible. For example, all the work that goes into designing the minimum viable product is—until the moment that product is shipped—just WIP inventory. Incomplete designs, not-yet-validated assumptions, and most business plans are WIP. Almost every Lean Startup technique we’ve discussed so far works its magic in two ways: by converting push methods to pull and reducing batch size. Both have the net effect of reducing WIP.
In manufacturing, pull is used primarily to make sure production processes are tuned to levels of customer demand. Without this, factories can wind up making much more—or much less—of a product than customers really want. However, applying this approach to developing new products is not straightforward. Some people misunderstand the Lean Startup model as simply applying pull to customer wants. This assumes that customers could tell us what products to build and that this would act as the pull signal to product development to make them.9
As was mentioned earlier, this is not the way the Lean Startup model works, because customers often don’t know what they want. Our goal in building products is to be able to run experiments that will help us learn how to build a sustainable business. Thus, the right way to think about the product development process in a Lean Startup is that it is responding to pull requests in the form of experiments that need to be run.
As soon as we formulate a hypothesis that we want to test, the product development team