Evil as Predatory Symbiosis
Despite all the realistic details of the family dynamic, King maintains the supernatural element through to the end without explaining it away at the end. The Overlook is haunted and there is a force of evil at work within it. But that force is not overpowering enough to simply turn good people into evil. In order for its dark powers to wield influence, there must be a fundamental character flaw with a direct association to a strong potential for malevolence within its victims. Thus, the Overlook is like a predatory parasite that—rather ironically—is constantly on the search for a host with a weakened immune system. Jack’s alcoholism is the entry point in his particular case.
Failure of the Caretaker
Jack is woefully inadequate as the winter caretaker. After all, the Overlook has survived employing caretakers for three-quarters of a century without a boiler explosion burning the place to cinders. When the caretaker fails, things fall apart. The same holds true for Jack’s job performance as caretaker of his family. He is not a total failure in that regard; in his more lucid moments Jack shows genuine tenderness for his wife and son and does try as hard as he can. The problem is that the best he can do is not up to the task of keeping that family from falling apart. Jack may have always been the caretaker, but that does not necessarily mean he is the right man for the job.
Addiction
Jack is a recovering alcoholic. Spoiler alert: the recovery isn’t going as well as one might expect inside an isolated hotel with no access to liquor. The novel explores themes associated with the consequences of addiction using Jack’s alcoholism merely as a starting point. Jack becomes briefly obsessed with carrying out his caretaking responsibilities before stumbling across the scrapbook which becomes a new and increasingly more powerful addiction. Addiction to alcohol and drugs can also be interpreted as forms of isolation and entrapment and so the living conditions within the Overlook serve to become a commentary upon the nature of addiction and the powerfully conflicting urges to give in and fight off those illicit desires.