All hell breaks loose

"When have any of our plans ever worked? We plan. We get there. All hell breaks loose."

Harry says that to Hermione in The Deathly Hallows, Part 2, just after they've escaped Gringott's with Hufflepuff's Cup. He's told them that Voldemort knows they're hunting Horcruxes and that the final one can be found at Hogwarts.

When Hermione objects to the idea of going immediately to the school, saying they should plan instead, Harry responds, "When have any of our plans ever worked? We plan. We got there. All hell breaks loose."

Harry's right of course but it's an interesting line for the screenwriter, Steven Kloves, to have added to the story (it's not in the novel). Why does he throw this line in, since in some ways it sounds to me like a criticism of Rowling's books?

I doubt he intended to criticise Rowling in any way. I think he puts it in because he needs a quick explanation for why they have to go to Hogwarts immediately, without planning.

In the novel, the explanation is much deeper and more subtle. Voldemort realises they're hunting Horcruxes and decides that he has to visit the site at which he's hidden each of the others to confirm that they are still there.

Harry sees inside his mind as Voldemort thinks of each one and makes the decision to leave the one hidden at Hogwarts until last, feeling that it must be safe there with Snape in charge.

That gives the Hero Trio some time to get to Hogwarts and begin the search, while the Dark Lord is visiting his grandfather's shack and the cave by the sea.

They can't plan because they would be wasting the precious time granted them by Voldemort's search. It's a much more plausible and interesting explanation.

But, of course, the movie Harry is right. No matter how hard they plan, they always seem to survive on their wits alone.