Creator Backlash: Jack Nicholson and Shelley Duvall both resented how praise for the movie focused almost entirely on Kubrick's direction and not on their performances. Nicholson, who is actually not a psychopath in real life, was particularly offended on Duvall's behalf, saying that hers was the most difficult role he had ever seen an actor take on.
Disowned Adaptation: Stephen King had problems with the movie, feeling that his novel's important themes, such as the disintegration of the family and the dangers of alcoholism, were ignored. He was also opposed to the casting of Jack Nicholson and Shelley Duvall. Over the years, he's warmed to the film, even calling it one of his favorite films...though he still doesn't think it's a very faithful adaptation. (to the point he produced a TV miniseries that goes closer to the book - and is derided for barely holding a candle to Kubrick's film)
Kubrick would loudly berate Shelley Duvall (Wendy) whenever the slightest thing went wrong, in order to make her feel as distressed as the character. Jack Nicholson realized this, but resisted the urge to just give her a hug which probably helped her freak out effectively when Jack came after her with an ax. When Duvall reflected on this experience, she eventually realized that Kubrick was actually getting the best out of her, but she didn't want to go through a similar experience.
Scatman Crothers was allegedly reduced to tears because of Kubrick's insistence on getting absolutely perfect takes - it's debatable whether to chalk this up to this trope or Kubrick simply being a Prima Donna Director.
A documentary states that most takes with Jack Nicholson are among the 20th takes, after the actor got tired and started ramping up the madness of his performance even further.
Inverted with Danny Lloyd, the child actor. Kubrick was very protective of the boy and was genuinely concerned that the dark elements of the movie would traumatize him. So he treated each scene with Danny like it was a playful game, and shielded him from the true nature of the movie.
Throw It In: In one scene, Jack Nicholson yells "Here's Johnny!" while poking his head through a door, and Stanley Kubrick, after having the joke explained to him (he'd been living in England since before Carson started hosting The Tonight Show), decided it worked. Jack's "Three Little Pigs" references were similarly improvised.
Made slightly more alarming by the fact that Jack Nicholson had been a volunteer fire marshal at one point and tore down the door far too easily the first time, thus causing them to have to build a stronger one.
The original script specified that "Jack is not working." The part in which Jack Torrance throws a tennis ball around the Overlook Hotel was Jack Nicholson's idea. Likewise, Danny Lloyd came up with the idea of moving his finger while talking as Tony, as he spontaneously did it during his first audition.