186 THETOYOTAWAYFIELDBOOK
Poka Yoke
Workers are assisted with the prevention of mistakes by the utilization of poka
yokemethods or devices. This term is generally translated into English as “mistake
proofing” or “error proofing.” Error proofing is not so much a lean “tool” as it
is a way of thinking and evaluating problems. It is based on the philosophy that
people do not intentionally make mistakes or perform the work incorrectly, but
for various reasons mistakes can and do occur.
There is a significant difference in the Toyota Way of thinking about the causes
of mistakes and the thought process used within other companies. In our work
with other companies, everyone unanimously agrees, “People make mistakes.” It
is also unanimously agreed, “If people paid attentionthey would not make as many
errors.” Conventional thinking tends toward identifying the cause of mistakes as
“human error,” while the Toyota Way always starts with the assumption that an
error is a failure of the systemandmethodsthat are used to perform the work. Quite
simply, errors occur because the current method allows them!
The difference in thinking shifts the responsibility for errors from the people
to the method, which also shifts the blame for mistakes from people to systems.
When people are released from blame, they are free to focus on creating more
effective systems and actually solving problems, rather than defending them-
selves. It is common within Toyota for a manager to apologize to a worker when
the worker makes an error, because management bears the responsibility for
creating effective systems that prevent mistakes. When was the last time someone
in your company apologized to a worker when the worker made a mistake?
The following case example typifies the thinking within most organizations.
TIP
Don’t Give People Rules They’re Unable to Follow
This tip applies in many ways, but in this case it relates to the rule of
never knowingly passing defects to following processes. This
involves more than just telling people not to do it. What do they do
if they find a defect? Who do they call? Where do they put it? If these
issues are not defined, the people will be confused and conflicted.
They want to do the right thing and follow instructions, but if it isn’t
possible to follow the rule andget the job done effectively, they will
choose to get the job done and violate the rule. Watch to see what
happens. Try the task yourself to get firsthand experience. Don’t
assume that people break the rules because they don’t care. Maybe
there is not a good system for helping people to follow the rules.