Abstract: Changing cultures within organizations has proven very difficult to achieve through top-down mandates and directives alone. However, some companies have succeeded in catalyzing large-scale cultural transformations by taking a different approach - sparking grassroots movements from within. This practitioner research brief examines why movements are more effective than mandates at shifting underlying organizational mindsets and norms in lasting ways. Drawing on theories of self-determination, diffusion of innovations, and lessons from impactful social movements, it explores how leaders can cultivate internal change agents to champion a compelling vision that aligns with employees' intrinsic values and purposes. Case examples from Southwest Airlines and healthcare demonstrate how grassroots pioneering, not administrative edicts, fundamentally reshaped entire industries over time. The brief concludes by advising leaders seeking profound cultural change to empower bottom-up movements rather than attempting to force compliance through top-down mandates.