  Quantum mechanical wave functions have phases. These phases either initial or
acquired during time evolution usually do not enter the final expressions for
observable physical quantities. Nevertheless in many cases the observable
physical quantities implicitly depend on the phases. Hence we may regard the
phases as a sort of hidden variables of Quantum Mechanics. Neglecting the phase
role makes inexplicable the peculiar quantum effects such as particle
interference, Einstein-Podolsky-Rosen correlation and many others. To the
contrary the adequate inclusion of phases into consideration reduces QM puzzles
and mysteries to simple and obvious triviality.
