Although the United Nations (UN) Sustainable Development Goals (SDGs) express urgency for actions, the UN also reports that reaching these goals as planned is very challenging. It has been argued that a mindset paradigm shift is needed and this paper will show that knowledge management (KM) can play an important part in this shift. Knowledge of sustainability is often complex, systemic and hard to capture (tacit), leading to specific challenges in its management. To address these, a three-step process, DCA, had been proposed beginning with defining (D) what knowledge is needed, then collecting (C) and acting (A) upon it. Focusing specifically on the defining step (D) and on tacit knowledge as the most challenging aspects, the paper proposes two improvements: first, to integrate Nonaka et al’s SECI model (Socialize, Externalize, Combine, Internalize) that describes how tacit knowledge can be externalized and shared. Secondly, the Sustainability Mindset by Rimanoczy is proposed as framework that aligns values and allows discovery and formulation of tacit sustainability knowledge along its content areas and principles. It is posited that when tacit understanding becomes more tangible, shifts in mindset can occur more readily, and vice versa, that a broadened mindset eases sense-making of tacit knowledge, thus creating a cycle of growth and change for the organization. The Sustainability Mindset Indicator (SMI), a personal development tool is proposed to operationalize the development of the sustainability mindset, and said exploration of tacit knowledge, which combined with tools from the SECI model may offer managers concrete tools to define the knowledge their organizations need on their pathway to change towards sustainability and fulfillment of SDGs.