Art thou not, fatal vision, sensible To feeling as to sight? or art thou but A dagger of the mind, a false creation. Proceeding from the heat-oppressed brain?

The lines you provided are from William Shakespeare's play "Macbeth." The character Macbeth is questioning whether the dagger he sees is a real, tangible object or just a product of his troubled mind. This reflects his internal conflict and the psychological turmoil he is experiencing. The dagger is a symbolic element representing his inner struggles and the influence of his ambitious and guilt-ridden thoughts.