Hyde to support the universal theory that all humans have a natural duality and that there is good and evil in everything. In the critical essay, Jekyll and Hyde and the Double Brain by Robert Louis Stevenson, Anne Stiles further criticizes the features of the short story when she states: "Like these scientists, Stevenson explores the potentially heretical possibility that human beings are inherently double , even in a state of health. .According to Jekyll's narration, he and Hyde existed before the discovery of salt which allows them to lead separate lives” (Stiles 4). Jekyll is aware of his desire for the wicked and seeks a way to separate good from evil. Just as drugs dull the pain of addicts, the salt Jekyll adds to the potion dulls the stress of duality in his own mind. He abuses his body to escape the chains of his own mind and not feel the guilt of wanting to be malicious. Whether healthy or mentally ill, Jekyll is a concrete example of the duality inherent in the human spirit. Additionally, Stevenson incorporates an expansion of the duality of good versus evil. In Dr. Jekyll and Mr. Hyde, Thomason reveals: "Stevenson argues that the novel is 'a symbolic representation of the dual nature of man, with the morality reversed: not to impress us with the victory of good or evil , but to warn us.” us of the strength and ultimate triumph of evil over good once sin is allowed to enter human habitation” (Thomason 9). It is obvious that Dr. Jekyll is a prestigious example of the fact that humans do not know their own strength mentally, nor their own physical strength. In Jekyll's honest attempt to separate good from evil, evil took over good. Evil, Edward Hyde, won the greatest victory over good, Henry Jekyll, by being fatal to both.