Evolution operator shows that state evolves deterministically and doesn't hide randomness anywhere. You use probabilities when you want to explain human experie

Evolution operator shows that state evolves deterministically and doesn't hide randomness anywhere. You use probabilities when you want to explain human experience, because you can't practically compute human's state. But you don't strictly need fundamental randomness for this optimization, Bayesian probabilities work in the same way, whether randomness is fundamental or not is difficult to observe. That said, computational difficulties start in the measurement device, that's where you should do collapse if you don't want exponentially complex calculations. Outcomes of observation are explained by linearity of evolution operator and decoherence, but then you get human factor: different people have different problems with this explanation, I think it's because unitary motion is unintuitive, Aristotle knew explanation of heliocentrism, but it didn't work, because geocentrism was more intuitive for him. Some apparently suggest that to explain human experience you need to calculate mind from physics, which needs to solve the hard problem of consciousness, which is impossible.