This work establishes the principle of source inaccessibility as a general structural condition of scientific knowledge. Across all scientific disciplines, empirical data do not provide direct access to an underlying source or system. Instead, observations arise as structured traces produced through interface-constrained interactions. We show that the standard assumption of source accessibility relies on an implicit epistemic leap: the unjustified interpretation of observational processes as invertible mappings. Formally, the observational process is represented as a mapping from interactions to a space of registrations. In general, this mapping is non-invertible, and therefore observations determine not a unique source, but an equivalence class of admissible interactions. As a consequence, objects, laws, invariants, and statistical constructs cannot be interpreted as properties of an underlying reality. They must be understood as operator-dependent structures defined within the space of registrations. We develop an alternative framework in which admissible regions replace state-based representations, and knowledge is grounded in the identification of stable structures within these regions. Classical constructs—including filtering, statistical estimation, and state-space models—are reinterpreted as operations acting on admissible regions rather than as procedures recovering hidden states. The analysis is supported by cross-disciplinary evidence from physics, chemistry, biology, medicine, economics, machine learning, history, psychology, and sociology, demonstrating that the absence of direct access to sources is not domain-specific but universal. This work motivates the development of a General Interface Epistemology of Science, in which the primary objects of analysis are regions of admissible registrations and their transformations. A formal counterpart to this framework is developed in: Nekludoff, Alexey A.Consequences of the Ontology of Dynamics (in Russian)DOI: https://doi.org/10.5281/zenodo.18213382 where admissible regions, closure operators, and their role in generating discrete structures are introduced within an interval-based formulation of dynamics.