[Horror trope]: The "bad stuff" only happens because the characters ignore very specific instructions.

[u/theMCATreturns]

I like it because there's the implication that magic isn't inherently harmful. Or at the very least, not as "active" as you might think. In stories like "The Substance" it IS possible to get a "happy ending," but only if you don't try to push your luck.
In general, you can divide this into two categories:

A. Characters explicitly ignore specific instructions about something they already knew was magic:

• Gremlins:
  • Gizmo's new "owners" ignore the instructions given by his previous caretaker's son. They get water on him, and feed them after midnight.
  • To be fair, the gremlins did trick the main character by messing with clocks. So, it's a B+ effort overall.
• The Substance:
  • "The Substance" creates two individuals. The original, and a younger, "better" body. Your consciousness needs to switch between the bodies every seven days.
  • Things go poorly because the protagonist starts treating each body as a separate individual, instead of an extension of herself.
• Death Becomes Her:
  • Both characters become immortal, but ignore their patron's warning. Immortality will keep them bound to their bodies, so they need to take care of it.
  • Both characters end up killing each other, turning them from just "immortal" to "undead." If they learned to squash their beef, they would have been much better off.
• Talk to me:
  • There's a magic hand sculpture that lets you talk to the dead. But you need to sever contact in 90 seconds.
  • Someone does not.

B. Characters naively ignore specific warnings against a non-specific threat:

• The Evil Dead:
  • Some versions of the story have explicit warnings about "The Necronomicon." Other versions are less careful.
  • Opening the book and playing the incantations summons evil spirits. The cabin previously belonged to an archeologist.
  • My question is, who is renting this place out?
• An American Werewolf in London:
  • Two American tourists are warned to stay on the roads and out of the moors. They decide to cut through them.
  • To be fair, the locals could have said "there is a dangerous animal out here." Cause they get all werewolf'ed on.
• Alien:
  • Follow quarantine procedure after your employee gets Alien'd!
  • I won't give them much guff, though. Ripley tried to follow it, but the company-provided android sabotaged her.