If you use the Lean methodology to improve a process that is plagued with frequent defects, errors, mishaps, failures, etc., that have eluded managers and engineers to the point where they just accept that there is no solution, you end up with a less desirable product because you cut corners and features to avoid the defects rather than ﬁx them.
Six Sigma is ideal for solving hard process problems that result in defects in the process output; e.g., broken windshields on cars coming off an assembly line, customer bills calculated incorrectly, data missing off a mainframe server, food getting spoiled long before its expiration date, etc..
Lean tools and methodologies lack the rigor to determine the root cause of elusive defect problems; Six Sigma tools and methodologies are too time consuming and costly to just to improve business efﬁciency.I don't know where people get this stuff. Who ever said in Lean or the Toyota Production System that you cut corners to "avoid defects" rather than fixing them?
Who said Lean doesn't help you find a root cause?
The reality is: fishbone diagrams, the "5 Whys," going to the gemba, andon cords, mistake proofing... these are all great examples of how we find and prevent defects in the Lean methodology.
Black Belts should really stick to writing about Six Sigma. There's a reason I stick to writing about Lean...