For companies seeking large-scale operational improvements, all roads lead to Toyota. Each year, thousands of executives tour its facilities to learn how lean production—the operational and organizational innovations the automaker pioneered—might help their own companies. During the past 20 years, lean has become, along with Six Sigma, one of two kinds of prominent performance-improvement programs adopted by global manufacturing and, more recently, service companies. Recently, organizations as diverse as steelmakers, insurance companies, and public-sector agencies have benefited from “leaning” their operations with Toyota’s now-classic approach: eliminating waste, variability, and inflexibility.

Yet in our experience, organizations overlook up to half of the potential savings when they implement or expand operational-improvement programs inspired by lean, Six Sigma, or both.¹ Some companies set their sights too low; others falter by implementing lean and other performance-enhancing tools without recognizing how existing performance-management systems or employee mind-sets might undermine them. Still others underestimate the level of senior-management involvement required; for example, they delegate responsibility for change programs to their lean experts or Six Sigma black belts—practitioners who are technically skilled but often lack the authority, capabilities, or numbers to make change stick.

The broader challenge underlying such problems is integrating the better-known “hard” operational...