“But we who live in prison, and in whose lives there is no event but sorrow, have to measure time by throbs of pain, and the record of bitter moments. We have nothing else to think of. Suffering ― curious as it may sound to you ― is the means by which we exist, because it is the only means by which we become conscious of existing; and the remembrance of suffering in the past is necessary to us as the warrant, the evidence, of our continued identity.”