Why do you think that Stevenson wrote The Strange Case of Dr. Jekyll and Mr. Hyde?
The history about how Stevenson's novel emerged might be as interesting as its premise. One reason Stevenson wrote The Strange Case of Dr. Jekyll and Mr. Hyde is because it came to him one night in a dream. One night, he was suffering from intense nightmares. They were so strong that his wife had to wake him:
In the small hours of one morning, [...] I was awakened by cries of horror from Louis. Thinking he had a nightmare, I awakened him. He said angrily: "Why did you wake me? I was dreaming a fine bogey tale." I had awakened him at the first transformation scene.
Stevenson could not shake how the story came to him, envisioning it before it was written. The artistic belief that something organically imprinted had to be recognized as a form of inspiration seized Stevenson. It is for this reason that he was able to compose the drafts of the book so quickly.
Another reason Stevenson wrote The Strange Case of Dr. Jekyll and Mr. Hyde was because the subject matter intrigued him. Stevenson was driven by the need to explore the different polarities that existed within human beings. Stevenson gives voice to this compulsion through Jekyll's own words:
With every day, and for both sides of my intelligence, the moral and the intellectual, I thus drew steadily nearer to that truth, by whose partial discovery I have been doomed ... that man is not truly one, but truly two ...
The "dual nature of man" is an idea that fascinated Stevenson. It plays out in how Stevenson wrote the novel. While very sick and bed-ridden, Stevenson worked at an intensely fast pace, creating prodigious amounts of work in the process. This duality of someone sick and yet able to produce so much is a reflection of the same type of binary reality that governs the novel's premise. From one evening's nightmare, Stevenson found himself driven to create what would end up becoming the novel.