Monday, July 11, 2011

Explaining why Limiting WIP is so important

According to Kanban limiting Work In Progress is a foundational component that enables knowledge workers to engage in continuous improvement. But why? And how do I explain the need to limit WIP to execs and other decision makers that need to be convinced?

Here's the arguments I've been presenting..

Limiting WIP leads to a virtuous cycle of improvement. Multi tasking goes down, feedback goes up, errors are easier to catch, work becomes easier to break up into smaller prices, which makes it easier to limit WIP, which mean multi tasking goes down, etc, etc,etc

Limiting WIP is extremely important to ensuring maximum throughput in any systems that face variability. This has been proven in relatively stable systems like manufacturing assembly lines. It's exponentially more true in dynamic systems like software delivery and integration. Think of a highway, when WIP is to high you get a traffic jam, at the same time ifthe highway is empty you get no throughput, there is an optimization at play here. But this is a bell curve, 100 full WIP is never the answer

Limiting WIP exposes bottlenecks in your process, when inventory is low, and a particular process becomes blocked or produces defective work, it causes downstream processes to become starved of work. This is a good thing, it's a signal to fix your system of work. Yes, work will be delayed in the short term, but only long enough to improve the system of work, which will accelerate throughput over time.


  1. Absolutely - the very first principle of Kanban is strong visualisation, to let you know where the problems are. Which is normally a problem in any knowledge work as a bunch of people sat in front of computers all look the same.

    Secondly, reducing WiP further exposes problems *by design*. Mike Rother puts it beautifully:
    "Anytime you start up a pull system, it will crash and burn within a short time. There will be glowing and charred pieces, so to speak. But it is precisely these charred and glowing pieces that tell you what you need to work on, step by step, in order to make the pull system function as intended. Your second attempt to make that pull system work may then last a bit longer than the first, but it too will soon fail. And again you will learn what you need to work on. This cycle will actually repeat, albeit with longer intervals between the problems, until someday you have a 1×1 flow and no longer need the pull system."

    However, the huge power of reducing WiP is not in stopping multitasking, or avoiding motorway jams, or reducing cycle times (useful though all of those are). It is reducing Overproduction, which Masaaki Imai describes as a crime, and I don't think he was entirely writing metaphorically. It is by *far* the worst waste, and leads to unnecessary Inventory (itself a waste), Waiting, Transport as well as Unevenness and Overburden.

    Given some quiet time over Christmas, I may write something that explains all the benefits of a Kanban system - they're a *lot* wider than many people realise.

  2. Thank you for the kind comments Martin...