If you're not familiar with Bell's inequality, and the subsequent experiment, I suggest perusing over this summary. But essentially, an experiment is done with counting the number of electrons with certain spins, and applying that number to bells inequality, which dictates that the number of things with quality A and not B plus the number with B and not C will be greater than the number with B and not C. It is expected that the number of electrons with specific spins, and not spins, should corroborate with the innequality, assuming the following: 1. the validity of logic 2. objective reality 3. locality however the results of the experiment contradict the inequality. Thus, by reducto ad absurdum, one or more of those three assumptions must be wrong. Personally, I'd prefer to believe that we've somehow misconceptualized what spin is, or we've made a mistake in assuming that spin can be considered a quality, or that an electron can be considered an individual with individual qualities, than concede one of those three assumptions. However, if forced to bite the bullet, what assumption do you think would be the first to go.