The Demon in Process Religion

(excerpted from The Pipeline)


“Let’s pick up where we left off”, said the intrepid, results-based consultant.  “From a production perspective, what do we need to understand about processes?”

“The first area on my list is variation and uncertainty”, said the VP of Construction.

“One of the principles of Lean is to remove waste from the value stream”, he said.  “Variation is a form of that waste, and Lean attacks waste with kaizen and PDCA.  In some improvement circles, the principles of Lean and Six Sigma have been blended into Lean Six Sigma, and the Six Sigma portion of LSS focuses on removing variation from processes.

“But – if this is process religion, then the demon is named Murphy.

“If something can go wrong, it invariably will go wrong.  And – it will go wrong at the worst possible time.  We see it over and over and over again, and the result is uneven flow and long cycle times.  Maybe some other stuff I don’t even understand yet.”

“I take it that you think Murphy is somehow different, or is deserving of special consideration?”, the intrepid, results-based consultant asked, writing as she spoke:


“Yes, from this standpoint”, he said.  “There are two kinds of variation.  There is common cause variation and there is special cause variation.  The attributable variation – or common cause variation – is largely what Lean attacks with its kaizen and PDCA.  The natural variation – or special cause variation – is different;  it is more akin to uncertainty, and usually it is beyond our control.  I want to know how our system protects itself – how it buffers itself – from both variation and uncertainty.”

“Having an understanding of variation and uncertainty is important”, said the intrepid, results-based consultant, “because variation lies at the heart of every other production principle.  It affects everything.  The elements of a production system – the elements of production processes – are largely driven by the need to control variation and deal with uncertainty.

“And – yes – there is a difference between variation and uncertainty.  The common cause type of variation is a reflection of our ability – or our inability – to achieve repeatable results, while uncertainty, what we call special cause variation, is a reflection of not knowing what the results will be.  Uncertainty is about risk.  It is unexpected.  Uncertainty is what causes results to extend beyond the range of normal variation.”

“The point is – whether you’re dealing with variation or dealing with uncertainty – you still have to protect the system from its effects.”


(The Pipeline: A Picture of Homebuilding Production is available on the publisher website (, through the author website (, as well as,, and