Modern Man has the unavoidable freedom and capability - and, potentially, the curse! - of creating his own reality; as we see all around us as a matter of daily observation.
But this creating of reality is actually a co-creation; or (as Owen Barfield terms it) a participation.
In other words; we are each creating our own reality, but using the 'material' of God's ongoing divine creation.
What this means is that our personal creation may be in-harmony-with pre-existing divine creation, with the knowable universe... Or against it.
Each Being, including ourselves, can know the universe only by his own participation in it: All possible knowledge is participation, because uncreated reality is unknowable (unknowable because it is purposeless, meaning-less chaos).
Therefore we must and do create the reality by-which we each live; but we can get it right - or wrong.
And getting it wrong means being on the side against God's creative purposes and methods.
In a world that is overall ruled by demonic powers; anyone who (whether passively, or actively) accepts this worldly ways of creating reality will, of course, be set-against divine creation.
When our thinking is 'mundane' - when it consists of 'facts' and concepts derived from this-worldly demonic sources; then naturally we will never become aware that our personal created world is a kind of evil delusion...
Only when our discerning and evaluating thinking is active, conscious, primary-thinking; thinking by our real, divine selves; will we know whether the world we personally-inhabit is true to God's creation - or against it.