"Classical" states (a single dot on the screen instead of an interference pattern) are created through the measurement process, which involves entanglement and

"Classical" states (a single dot on the screen instead of an interference pattern) are created through the measurement process, which involves entanglement and dephasing: The small quantum system (the electron) first becomes entangled with the macroscopic system (the photo film and everything coupled to it), then the phase coherence between the individual eigenvectors of the electron gets lost due to the coupling with a large number of degrees of freedom in the measurement system.