Agreed, I'd phrase it slightly differently in that symbolized reality exists inside our heads, but we often operate as if[1] it exists outside our heads and some, possibly a majority of people, believe that there is not difference - that they are in fact the same thing, that the symbolic universe is real universe.

Every frame is the act of assuming a symbolic correspondence. The only problem is that we've incredibly bad at disproving the veracity of frames.

1. To great success even