Lean needs Six Sigma because:

Six sigma needs Lean because

Lean cannot explain the role needed to start a project to attain specific results. It identifies waste.

Six Sigma sub-optimizes processes decrease process defect.

Delivering a collection of tools to know problems and sources of difference.

It improves process speed/cycle time

Lean does not identify the influence of deviation

It includes methods for continuous improvement (Kaizen)

Lean is not as strong in the measure and analyze stages of DMAIC

Six Sigma quality is approached faster if lean eliminate non-value-added steps