I upvoted you since I don&#x27;t know why you&#x27;re so far down the page.  What you say is essentially correct.  The error most people make when trying to understand quantum mechanics is assuming that the measuring system is independent of the measured system.  But the overall composite system can&#x27;t be factored like that since it evolves unitarily (and deterministically) into a state that isn&#x27;t representable as a tensor product.