Quantum Physics may seem complicated to understand. It is. The reason is not because of the math or science involved (even though that could be hard to grasp), it's because of the unbelievable philosophical implications that arise out of understanding it. Niels Bohr, a renowned physicist and author of Copenhagen Interpretation of Quantum Mechanics once said, "Anyone who is not shocked by quantum theory has not understood it."
Quantum physics tells us that two events in separate locations, may actually be the same event. Einstein was concerned by the implications of the wave-particle theory of quantum physics. He devised his own thought experiment (which has now been confirmed mathematically and experimentally).