The book is far more ambiguous about the Overlook Hotel and its ghosts than is immediately apparent (and far more subtle than most of King's books). The overwhelming majority of the events are passive, and it is trivial to chalk these events up to hallucinations or a child's runaway imagination.
Firstly, Danny starts to have his 'visions' once he is aware of the hotel, and before he is anywhere near it. This is an example of his precognition at work, but Dr. Edmonds points out that their family, and Danny in particular, has gone through a lot of trauma and upheaval that this small, intelligent boy is having a hard time coping with.
As time goes on, Danny sees violent and disturbing visions that start to occur with greater frequency and higher intensity. This understandably makes him scared and upset, and his inability to cope with this isolation and the increasing tension between family members only worsens Danny's situation. Convinced that there really is something spooky and dangerous happening, he finally snaps and chokes himself almost to death while in the midst of a panic attack.
Wendy has been somewhat more perceptive of Danny's state, and though skeptical at first, fear for her child makes her take Danny too seriously, to the point where she starts to believe in Danny's imaginative delusions of evil ghosts.
This is also exacerbated by the fact that Jack has been coping with sobriety and always aware of the failures in his life that have placed him in this situation. Once his son's hallucinations become disruptive and his wife starts to buy into it, all of Jack's problems become powerfully exacerbated by his fear that his family will be doomed if they abandon the hotel. It is this struggle, and not ghosts, which eventually drive him over the edge and become homicidal.
- There is one serious issue with this theory: Grady letting Jack out of the pantry. Wendy or Danny certainly didn't do it, they were nowhere near at the time and have no reason to let him out anyways, and the door is locked from the outside. This is more or less the only thing that cannot be explained away as hallucination or imagination, and instead does imply supernatural interference.
- It probably started as just room 217, but as it grew older and more powerful it took over the entire hotel. Likewise, the 1408 creature could eventually take over the entire Hotel Dolphin. The original room would remain the hub of the creature's consciousness, but as it grew it would get smarter and use subtler tricks to claim its victims so that people don't realize the whole structure is now evil instead of just the one haunted room.
- That might also explain why the Overlook did not become profitable until after Ulman took over as the manager, despite already having been around for decades at that point.
- Or, the hauntings only made themselves known to certain people, especially those who has a family member that has the Shining.
- This would help explain the hotel's intense interest in Danny, who presumably had some very strong steam.
- I think the symbolism is really much simpler then that. Red rum. Blood.
When the Overlook was first opened one Randall Flagg, perhaps under a different name, stayed at the hotel. Whether it was by his design or his simple presence there, he left a scar on the hotel which took up a life of its own and eventually became the enitity that tormented the Torrance family.
In the movie, Jack's lack of warmth toward Danny, rare displays of awkward affection, and seeming contempt are due to his jealousy that Danny - a child from Wendy's previous relationship - gets attention before him from Wendy.
I know it's kind of a minor one, but every time that he looks at Dick Hallorann it's either extremely brief (split-second) or he looks like he's pissed at the guy for a reason that even he doesn't realize. And then, of course, there's his encounter with Grady, and the bit of dialogue that he repeats regarding Dick.
Now, Wendy may have it, but it's much more suppressed than Jack or Danny's level of reading. But what sets it off and for her to be able to see the ghosts in the third act is the amount of fear she was suffering at that moment. Fear can cause the body to have certain biological reactions. Maybe the fact that the fear level caused by Jack finally going nuts and trying to kill her wakes up the Shine in her, even if it was just for that one particular moment.
That's just a hypothesis, but it would explain how Danny's ability is more apparent while both his parents seem to not have this ability (maybe because both parents aren't aware they have it).
- The book states that most mothers usually have some small amount of shine to them.
- Likewise, it's entirely possible Jack didn't actually die from frostbite/hypothermia - he merely SHIF Ted to a timeline where he had access to a Pod, then sent a copy of himself back to 1921.
Now, how does this apply to the Overlook? We only hear of one tragic event similar to what happens to the Torrence family: the Grady family. Other than the deaths of patrons at the hotel over the years, there are no indications of any other off-season murders in the same regard as we see with the Grady family and the Torrences, let alone any on-season hauntings of the magnitude that we see towards the end of the film. That may be because, much like the on-season, there's barely many people who have a high enough Shine that would charge up the ghost activity during that was hired previously. During the on-season, we know Dick Hallorann worked at the Overlook for years, but we don't know for certain if his Shine ability is as strong as Danny's. And anyone else who comes to the hotel who might have a strong enough Shine may not stay long enough for the supernatural activity to get strong enough to make itself noticeable and may have been rather limited to one area (something like a single hotel room with the number 237 on the door). However, for the Gradys, they may have had a pair of strong Shine users and not realize it: their twin daughters. Before that, the Overlook's hauntings may have been limited to one room. But when the Grady twins are staying inside the hotel for months during the off-season, it inadvertently charged up the hotel's supernatural abilities enough for ghosts to start appearing, first as simple visions until they got to th point they could physically manipulate things if they so choose, and eventually exceeding the limitations of Room 237. After Grady murdered his family and himself, the charge stayed for a little bit until it eventually died back down again to where it was limited to one room.
And like the Gradys, the Torrences brought Danny to the Overlook. The moment they moved in for the off-season was when the spiritual cell of the Overlook began to charge again. Like before, starting with visions. Eventually, it reached the point where Danny got attacked by the woman in 237, causing actual physical harm. And this explains how a ghost could let Jack out of the food locker: the Overlook's supernatural charge was at full enough at that moment that it allowed ghosts to be able to manipulate objects once again, and even allowed people without the Shine ability to see the horrors (this would explain how Wendy didn't see any ghosts or visions before the final act of the film).
So, that means they after Danny and Wendy escape in the snowcat, the strong charge the Overlook had slowly died out again. As for if management knew that strong Shine users could cause their hotel to become a massive Spook Central by staying in the hotel for months is hard to say. But it explains why there's no noted hauntings at the hotel in the film that occur during the on-season, other than what is limited to Room 237.
- Combine that with the theory above about the entire Torrence family having certain levels of Shine, it'd make sense that the combined abilities slowly woke the hotel's supernatural center up.
King would go on to explore the concept in far greater depth in It; the hotel isn't just an Eldritch Location, it was built above a full-blown Eldritch Abomination, one that (like It) feeds on fear and savagery, It slowly drives ordinary people insane and for those unlucky enough to "Shine" (have psychic abilities), it can open direct conduits to them. Hallorann could put up mental shields against it through long exposure, but a little kid? That he doesn't Go Mad from the Revelation speaks to both iron willpower and a major miracle. "REDRUM" is him channeling the Eldritch horror that infests the hotel. And those that go mad within its walls are like the victims of It and Its Deadlights; they are consumed by the hotel, to live within its walls forever more.