Lean is one of the biggest management ideas of the past 50 years. No less than Ford's original assembly line, it has transformed how leading companies think about operations - starting in assembly plants and other factory settings and moving more recently into services ranging from retailing and health care to financial services, IT, and even the public sector. Yet despite lean's trajectory, broad influence, and level of general familiarity among senior executives, it would be a mistake to think that it has reached its full potential.