Avalanche effect
Many sources of waste will induce others, and it is hard to tell where this chain reaction ends, as it causes an "avalanche effect". The following are some examples.
Overproduction - Extra features and junk stories increase the product and the release scope amounting to a bigger inventory. Big inventory - A big work in progress increases work complexity. A higher complexity for both problem and solution results in more defects. More defects introduce more unexpected interruptions of the work in progress and that produces more waiting. Waiting ...
Vicious circle
An even worse situation is a vicious circle effect between wastes. If wastes are not avoided, the difficulties not only persist but will increase in a never-ending spiral.
Task switching affects people's focus and that increases the number of defects. More defects amount to more unexpected interruptions, which results in more waiting. With more waiting, the delivery is delayed, and the target business changes more than we previously expected. With this extra time, we receive more change requests that will increase the release and the product scope (inventory). With a bigger inventory, task switching increases: we cannot good enough slice the work inside a release, we can't say that something is done and the work for different things will interfere.
A situation where the vicious circle could be even faster occurs when two wastes are directly feeding each other.
Task switching reduced focus and that in turn increases the number of defects. More defects amount to more unexpected interruptions, which in turn result in more task switching.
A lesson to be learned
We cannot disregard any important source of waste since each one creates and feeds other wastes.
Essential Lean Series
Read first: Principles of lean thinking (by Mary Poppendieck)
Essentializing Lean - essay
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