"know what we see rather than see what we know"

Abraham Heschel, in The Prophets: 

“What impairs our sight
           are habits of seeing
            as well as the mental concomitants
                             of seeing. 
Our sight is suffused with knowing, 
  instead of feeling painfully
                          the lack of knowing what we see. 
The principle to be kept in mind is
                  to know what we see
                       rather than to see  what we know.”
-Abraham J. Heschel, The Prophets: An Introduction. vol. 1 (New York: Harper & Row, 1962), p. xi.