symbols are designed to be conflated for reality. in our own minds we are interacting with the mental representations of external things and only the external reality by proxy of our mind.
cogito ergo sum and other such observations are just pointing out this basic truth: we live in our minds are interact with symbols as the primary objects of consciousness.
the higher-order symbolic systems, like narrative fiction, or mythology, are designed to run with this natural conflation and go beyond merely conflating the symbol with reality, but instead now conflating the symbol with SUPER reality. the symbol now stands for something better than the real. more meaningful, more beautiful, more true than reality could ever be. in other words, it becomes culture, which is more important to people whose lives are embedded within a cultural context than reality is to those people.
the really strange thing about this is that it is adaptive, up to a point. when your daily life is much more about navigating through a culture than it is about navigating through a wildnerness it is perfectly understandable why the cultural symbols become primary in their importance.
this can go too far, of course. the culture can be a deranged, destructive, rapacious, monster of a thing and we know what the consequences of that can be. still, it seems quite clear why stories carry the weight and importance that they do.