In the Einstein-Bohr debate, Einstein considered quantum mechanics incomplete and disagreed with Born’s probabilistic interpretation of wave-functions. Observers in the axioms of quantum mechanics also bothered Einstein. Inspired by Einstein, Bell and his followers intended to complete quantum mechanics within the framework of local realism. Regrettably, the deterministic correlation between distant components of a separable system in Einstein’s local-realist description of the world is mistaken for non-locality in the world described by Bell’s theorem, leading to incorrect interpretations of experimental results obtained by testing Bell inequalities. This article introduces a new principle, the general principle of measurements, which is proved as a mathematical theorem and allows quantum mechanics to be completed within the framework of local realism while keeping the formal axiomatic definition of a general Hilbert space unchanged. The completed theory can provide the same probabilistic predictions of empirical results as those provided by the current theory. Using disjunction (“or”) as the logical relation between superposed orthonormal vectors, the completed theory precludes observers in the axioms of the current theory and inexplicable collapses of wave-functions, thus it is intuitively comprehensible and alleviates much difficulty in understanding quantum mechanics. Among various world views, Einstein’s local-realist world view is correct.