The crux is that randomness is indistinguishable from a large collection of pre-determined hidden variables (imagine rolling all the dice for all of the outcomes of Physics ahead of time), but not all of the behaviors of quantum mechanics can be accounted for by (local) hidden variables (Bell's theorem.)
The crux is that randomness is indistinguishable from a large collection of pre-determined hidden variables (imagine rolling all the dice for all of the outcomes of Physics ahead of time), but not all of the behaviors of quantum mechanics can be accounted for by (local) hidden variables (Bell's theorem.)