This paper addresses the difficulty of generalizing Conant and Ashby's assertion that "a good regulator must be a model of the system," using examples from the field of artificial life. To overcome the limitations of existing theorems, we propose a new model concept that interprets an agent's behavior as "beliefs" and "updates" from the perspective of an observer. This provides a "model" of the system's environment, demonstrating its applicability to both classical control theory settings and internal state regulation. Seemingly counterexamples are resolved by interpreting the model as a simple case. The key point is that the model is not inherent to the system, but rather is imposed by an external observer.