The Magical Travel Mistake In Harry Potter And The Goblet Of Fire
For many young readers, Harry Potter and the Goblet of Fire was a turning point. It contained Voldemort's return and also featured the story's first prominent character death besides Harry's parents. The book also dramatically expanded the scope of the wizarding world, introducing readers to the Quidditch World Cup, the existence of other schools of magic, and new magical techniques like Portkeys.
Portkeys, which allow users to travel from one place to another, were just another addition to the bevy of options that witches and wizards already have to travel from one place to another. Witches and wizards who are of age can also apparate from one place to another, which is basically teleportation.
JK Rowling previously introduced floo powder in Harry Potter and the Chamber of Secrets. It's in that novel that Harry discovers that witches and wizards can travel between any two fireplaces by simply standing in a fireplace with a handful of floo powder and saying the name of the fireplace that you'd like to travel to. Harry has a little trouble with this his first time, but in general, it seems like a very convenient method of travel for witches and wizards of any age. In Goblet of Fire, though, Rowling breaks one of the rules she established two books earlier.
How Goblet of Fire breaks Rowling's travel rules
In Chamber of Secrets, Rowling makes it very clear that floo powder only works if every witch or wizard takes some, stands in the fireplace, and says the name of the place they want to go. Things break down for Harry Potter in that book because he doesn't say the name of the place he wants to go right.
In Goblet of Fire, though, when the Weasleys pick Harry up from the Dursleys' at Number 4 Privet Drive to take him to the Quidditch World Cup, the rules of floo powder seem to change slightly. As the Weasley family prepares to leave, Arthur puts a dab of floo powder in the fireplace that allows them all to travel back to the Burrow. After Arthur puts the floo powder in, the rest of the Weasleys just have to step into the fireplace to get transported back to the Burrow, without taking powder themselves or saying where they want to go.
This change is a break from the rules in Chamber of Secrets, where everyone has to arrange their own travel with floo powder by themselves. It's a shorthand that allows for Rowling to avoid explaining the rules of floo powder again, but one that bothers diehard fans obsessed with the intricacies of her magical world.