Final answer:
Dr. Jekyll loses control to Mr. Hyde due to a chemical imbalance caused by impure ingredients in his potion, leading to involuntary transformations. As Hyde's presence grows stronger, Jekyll becomes unable to revert to his original self, with Hyde eventually becoming the dominant personality.
Step-by-step explanation:
In Robert Louis Stevenson's novel The Strange Case of Dr. Jekyll and Mr. Hyde, Dr. Jekyll loses control over his alter ego, Mr. Hyde, due to an unintended chemical imbalance. Initially, Dr. Jekyll creates a potion that allows him voluntarily to transform into Mr. Hyde, his darker self, in order to experience life without the constraints of social morality. However, Jekyll's continued use and subsequent dependency on the potion lead to unexpected changes in the formula's effectiveness.
Specifically, impurities in the salt used in the potion resulted in the tonic working properly, and when Jekyll could no longer obtain the same impure salt, he found himself transforming into Hyde involuntarily and without the aid of the potion.
This loss of control symbolizes the struggle between the dual aspects of human nature and the consequences of unrestrained indulgence in one's baser instincts. Over time, Mr. Hyde grows stronger, and Dr. Jekyll's ability to revert to his original self diminishes until, eventually, Hyde becomes the dominant personality, requiring Jekyll to use the potion merely to revert to his civilized self. The more Jekyll becomes Hyde, the harder it is for him to revert back, leading to a hopeless battle with his dark side that he ultimately loses.