Quantum world is weird and that's an understatement. One of the theories explaining that weird world, called Copenhagen interpretation, shuns realism. Niels Bohr was the main proponent of that interpretation that made Einstein uncomfortable and spats between the two on the subject are legendary. As it turned it is clear until now that Einstein was incorrect. Another explanation for quantum mechanics was proposed by Hugh Everett in his PhD thesis, called Many-Worlds interpretation and was based on concept that myriad possibilities inherent in a quantum system each manifest in their own universe. That interpretation, summarily rejected by Niels Bohr, later made comeback but not soon enough for Everett, who gave up the field and went on to work for Pentagon for the rest of his life.
Ironically, Einstein's discovery of photoelectric effect saved scientific world from ultraviolet catastrophe and laid foundation of quantum field. But it was Niels Bohr and others' interpretation that turned Einstein against the uncertainty of quantum mechanics and until the very end he never reconciled with it. In between he unsuccessfully tried to poke many holes into quantum interpretation, with one of the most famous being EPR thought experiment. EPR stands for Einstein, Boris Podolsky, and Nathan Rosen. Einstein remained convinced that quantum uncertainty indicates incomplete understanding of reality. Nevertheless, the field thrived with contributions from likes of Erwin Schrödinger, Werner Heisenberg, Wolfgang Pauli, Paul Dirac and later John Wheeler, Richard Feynman, John Stewart. It has been long since that experiments have proven quantum entanglement, what Einstein used to call 'spooky action at distance' and is explained without violating the speed of light paradigm.
It maybe pointed out we live in a quantum world, without fully knowing how it works.