Page 197 - Lean six sigma demystified

176 Lean Six Sigma DemystifieD
? still struggling

Toyota says they don’t have a Six Sigma process, they just ask “Why?” five times.
ask: why does the process cause this error? get an answer and ask: why does
this answer cause the process to cause this error? get another answer and
repeat until you can go no farther. The answer to the last “why” is usually the
cause. Root cause analysis is easy for some people and hard to grasp for oth-
ers. The only way to understand it is to practice.

Fishbone Tar Pits

There are two main tar pits that teams fall into—whalebone diagrams and cir-
cular logic.

• A whalebone diagram (dozens or hundreds of bones) means that the
problem wasn’t focused enough in step 1. Go back and develop one more
pareto at a lower level of detail.
• Circular logic (C causes B causes A causes C again) invariably means the
logic wasn’t checked as it was developed. Remind participants to ask
Why? up to five times as you develop each “bone.” Then check your logic
each time you add a “bone” by working up the chain saying “B causes A.”
If the why of A is B but B does not cause A, then the logic is faulty. Cell

phones, for example, don’t cause false fire alarms. Cell phones cause RFI,
which causes unshielded detectors to go into alarm mode which causes
false fire alarms. Remind team members to verify their root causes before
proceeding.

Identify and Verify the Root Causes

Take away the cause, and the effect ceases.
—Cervantes

Like weeds, all problems have various root causes. Remove the roots, and like
magic, the weeds disappear.