Jay W. Forrester's original statement of the foundations of system dynamics emphasized four ‘threads’: computing technology, computer simulation, strategic decision making, and the role of feedback in complex systems. Subsequent work has expanded on these to expose the significance in the system dynamics approach of dynamic thinking, stock-and-flow thinking, operational thinking, and so on. But the foundation of systems thinking and system dynamics lies deeper than these and is often implicit or even ignored: it is the “endogenous point of view”. The paper begins with historical background, clarifies the endogenous point of view, illustrates with examples, and argues that the endogenous point of view is the sine qua non of systems approaches. What expert systems teachers and practitioners have to offer their students and the world is a set of tools, habits of thought, and skills enabling the discovery and understanding of endogenous sources of complex system behavior