The Copenhagen interpretation presumes the legitimacy of quantum superpositions, attaches ``the probabilistic nature'' to quantum mechanics, brings observers into axioms of the theory, and claims that quantum mechanics is already a complete theory. Einstein disagreed with this interpretation; he argued against the legitimacy of quantum superpositions, worried about observers in the axioms, and considered quantum mechanics incomplete. Inspired by Einstein, Bell and his followers intended to complete quantum mechanics within the framework of local realism. They derived Bell inequalities, tested them by experiments, and proved Bell's theorem to interpret the experimental results. Regrettably, the experimental results are misinterpreted. This article introduces a new principle, the general principle of measurements, and provides its mathematical proof. Based on this principle, quantum mechanics can be completed within the framework of local realism by using disjunction (``or'') as the logical relation between orthonormal vectors spanning any given Hilbert space while keeping its general definition unchanged. Probabilistic predictions given by the completed theory and the current theory are exactly the same. Furthermore, by eliminating observers from the axioms and precluding inexplicable collapses of wave-functions, the completed theory alleviates much difficulty in understanding quantum mechanics and is intuitively comprehensible. In conclusion, Einstein's local-realist world-view is correct.