We need to find out the sources of waste, but that requires a very good and close observation of the overall process. Some wastes, tough are important, are difficult to identify. For example:
- It is difficult to find that you have a lot of extra features or junk stories in your product.
- It is difficult to find that you have a lot of hidden work (for example product parts that are hard to read or are hard to change because of the technical debt)
Some other sources of waste are easier to detect, and are induced by most of the others (see "Avalanche effect"):
This means that, although we could successfully use Waiting and Defects wastes as red flags, finally we need to identify and eliminate the root causes. We should also remember that we cannot reduce the Lean goal of avoiding waste only to these two sources. Waiting is the main subject for the methods that use a visual control of the work. However, if something is harder to draw, it does not means that it is less important. There is no generic ranking between the main sources of waste and their impact is different from one context situation to another.
Essential Lean Series
Read first: Principles of lean thinking (by Mary Poppendieck)
Essentializing Lean - essay
Essential Lean - Red Flags