On the basis of quantum-mechanical realism and the philosophical view that "determinism and indeterminism are mutually dual and symbiotically coexisting," philosophical and physical perspectives are integrated to propose the "constraint—uncertainty" hypothesis in this paper. Combined with a temporal ontology of "a determined history and an open future," a unified interpretative framework for quantum phenomena is established. First, in conjunction with experimental results on fullerene quantum interference and spin decoherence in diamond NV centers, the core hypothesis is proposed: when a system is subject to a single dominant constraint, its behavior exhibits deterministic characteristics and uncertainty is suppressed; when subject to multiple competing constraints, its behavior becomes indeterministic and determinism is weakened. It is further clarified that the "constraint" in this work refers to a physically real underlying dynamical mechanism. Second, based on this hypothesis and temporal ontology, a self-consistent interpretation is provided for quantum phenomena such as wave-function superposition and quantum entanglement. It is argued that the "constraint—uncertainty" hypothesis offers an ontological basis for the Heisenberg uncertainty principle, thereby correcting the imprecise characterization in mainstream quantum theory that reduces uncertainty to an intrinsic property of particles. This paper further explores the tension between quantum mechanics and general relativity, suggesting that they correspond to different physical regimes governed by distinct constraint structures. A complete constraint-based model should naturally incorporate gravity, potentially offering a new perspective for the unification of the two theories.