The concept that **the underlying structure of anything will determine its behavior** is presented as one of the most profound and major points of the "Introduction to Structural Thinking". This statement serves as the **core principle** within the larger framework of Structural Thinking, distinguishing it significantly from conventional approaches to understanding and addressing challenges.

Here's how this core principle is elaborated in the sources:

*   **Contrast with Situational Thinking and Problem-Solving**: Most individuals and organizations tend to think *situationally*, focusing on immediate problems rather than the deeper underlying structures. Companies often pride themselves on being "dedicated problem solvers," but the sources argue that **problem-solving is not creating, and creating is not problem-solving**. You can eliminate all existing problems and still not achieve desired outcomes if the underlying structure remains unchanged.
*   **Implications for Change Efforts**: This core principle explains why many change initiatives, even good ones like the quality movement inspired by Deming, ultimately fail or are rejected by organizations over time, much like a body rejects an implanted organ. The reasoning is that **if the underlying structure is not conducive to change, the organization will reject it, regardless of how good the change effort might be**. Conversely, a **change of underlying structure almost invariably leads to a change of behavior**. The typical Western approach of immediately asking "how do we change it?" is deemed less effective than first asking "how do we understand what's giving rise to the predictable patterns of behavior that we're seeing?".
*   **Two Patterns of Behavior from Structure**: The underlying structure is responsible for two distinct patterns of behavior:
    *   **Oscillation**: This pattern describes a scenario where an individual or organization pursues a goal, may achieve it for a period, but then experiences a reversal, ending up without what was initially sought. Examples in industry include the cycles of building up capacity then downsizing, centralizing then decentralizing decisions, or engaging in acquisition sprees followed by divestment. While oscillation can be suitable in specific contexts, such as a rocking chair, it is deemed a **"terrible structure for personal life or for a company"**. This pattern clarifies why consultants might perform their "best work," only to find it undone years later; it's not a personal failing but a result of not making an adequate change to the underlying structure to create sustainability.
    *   **Resolving Advancing Structure**: In contrast, this structure leads to an **outcome-oriented approach**. Instead of being driven by problems, an organization focuses on defining desired outcomes, assessing its current state relative to those outcomes, and then determining the most effective path to move from the current state to the desired state. This requires clear understanding of both the desired outcome and the current reality, along with an iterative learning process to adapt as reality changes.
*   **The Dynamic of Tension and Equilibrium**: At the heart of structural behavior is the principle that **structure seeks equilibrium**. This drive for equilibrium is the dynamic force that causes things to happen. **Tension** is defined not as stress or anxiety, but as a **"structure of a contrast between a desired state and an actual state"**. This difference creates a state of non-equilibrium, which then naturally seeks equilibrium. In a proper creative process, the current state is brought into alignment with the desired state, achieving a state of equality or equilibrium.

In essence, the core principle of "underlying structure determines behavior" provides the foundational understanding for all subsequent steps in Structural Thinking, guiding the practitioner to look beyond surface-level issues to identify and address the fundamental dynamics that shape predictable patterns of behavior.