If you've ever struggled with writing the middle of your book, it's because you lack this structure. Fortunately, the solution is simple. Have your protagonists arrive at their goal in the middle of the book.
This might seem crazy. After all, they're supposed to confront their goals at the end of the book, right? If they arrive in the middle, that would be the end of the book!
Nope. Because that's when everything goes wrong. That's when your characters fail so spectacularly that now everything is worse.
Just read a brilliant reddit post about how to keep the middle part of your novel exciting. The key point:
What do you think?