By the time Egypt was subjected to the plague of darkness, they already knew it was over because that plague essentially told the Egyptians they had no power. Once they lost the power of the sun, they realized that they were impoverished from their power. The plague on the firstborn was the greatest and most powerful of all the plagues in Egypt. The firstborn of every family is the main spiritual power in that family. Adam was the first firstborn to exist and because of his corruption, that firstborn right was given out to his descendents. It went on to Avraham, but he had to purify it for it to have any use. Through Egypt, the firstborn of creation was restored. Israel went into Egypt itself and through the enslavement they purified this tremendous corruption the nations of the world brought on the Shechina and the entire light of spirituality itself. The plague on the firstborn is the loss of the firstborn of creation from Egypt which they had from the power of being notel kilkul kulam. They lost it to the People of Israel, who became the firstborn of creation.