The devil, having an angelic nature, knows how to trap us poor humans. We must remember that the devil was the highest angel and his nature didn’t change with his fall, albeit that he is blind with his pride. The devil tempted Eve with pride, and Adam fell through pride, by caring more about Eve than he did about God. Thus, humans, through the fall of Adam, are blind. The will is blind and needs the intellect to inform it, and pride is blind, thus, we have a sort of double blindness.