Hope. Pandora brought the jar with the evils and opened it. It was the gods' gift to man, on the outside a beautiful, enticing gift, called the "lucky jar." Then all the evils, those lively, winged beings, flew out of it. Since that time, they roam around and do harm to men by day and night. One single evil had not yet slipped out of the jar. As Zeus had wished, Pandora slammed the top down and it remained inside. So now man has the lucky jar in his house forever and thinks the world of the treasure. It is at his service; he reaches for it when he fancies it. For he does not know that that jar which Pandora brought was the jar of evils, and he takes the remaining evil for the greatest worldly good--it is hope, for Zeus did not want man to throw his life away, no matter how much the other evils might torment him, but rather to go on letting himself be tormented anew. To that end, he gives man hope. In truth, it is the most evil of evils because it prolongs man's torment.
~Friedrich Nietzsche