Rule 17 Of Fiction

Rule 17: ANYTHING can happen in the realm of fiction.

 Rule 18: Don't ask about what happened to the other rules before 17.

Rule 17 Of Fiction is a statement that anybody who works with fiction should live by: anything can happen in the realm of fiction. Feel free to spice that "anything" up however you want. Rule 17 Of Fiction can be compared to Rule 34 but with less porn: "If it can happen, it eventually will happen."

Why Rule 17 isn't used all the time
The story. If not for the story, you'd have people throwing fireballs, flying, destroying planets just by thinking about it, summoning dinosaurs, being invincible, breathing underwater, instantly killing their enemies, firing water out of their hands or mouths to cancel out the aforementioned thrown fireballs, bringing in characters from other franchises, and ruining the fabric of reality all the time.