Others have provided good examples, but I'll put it in a way that might make more sense, albeit with a slightly less correct simplification. >So what I dont ge

Others have provided good examples, but I'll put it in a way that might make more sense, albeit with a slightly less correct simplification. >So what I dont get is why QM you could argue that there is some hidden shared state. Because when you measure one of the coins in a particular way, there's an established probability that you'll change it some percentage of the time. (I.e. if you measure in this way 100 pre-prepared heads, you'll get some percentage of tails. [think of this as say measuring polarization of some photons after they've passed through a filter oriented to 0 degrees, by then placing a filter oriented at 45 degrees and seeing how many go through) However, even after you do that measurement, you'll find that the other entangled photons are still correlated with the result of the ones you measured. So there's something "extra" going on, which is QM entanglement. I.e. that shared state. You can actually see the effect of the "changing states" (not really what's going on, but if you were assuming the behavior was classical, it's what you'd start with. If you place two polarized filters at 90 degrees to each other and shine a light through it, you'll get basically zero photons out. Then, without changing anything else, you can put a third filter in-between the two but oriented 45 degrees from the others, and all of a sudden, about 25% of the light will pass all the way through the three filters! It's pretty cool. You could explain THAT part classically by saying that you are "changing the state of some of the photons by measuring them". But then... if you do that, you can't explain the correlation that happens when you do that with entangled photons, and classical explanations just don't really cut it unless you give up something like non-locality.