In the introduction, hugely famous fantasy writer Terry Brooks writes about the importance of outlining, so that you can make sure you get your story right. He deemed this pre-writing part as "Puzzle-building without a box cover," and I really loved that phrase.
Because it's true. In all of our stories, we are pulling characters and plot points--the puzzle pieces--out of nowhere and trying to fit them together in a way that makes sense. When it's all said and done, we want to be able to glue those pieces together permanently and frame up that puzzle (or, preferably, to see it on a shelf in Barnes and Noble or Borders). The reason I love the box cover-less puzzle analogy is because it expresses how truly unique and challenging it is to write a good book. Imagine dumping a 10,000-piece puzzle of an ocean full of colorful fish on a table and trying to solve it with no point of reference. Daunting, huh?
You set out to completing it, though, because you've bought the puzzle (thought up a story you can't ignore) and feel it inside that this puzzle will not go away until it's finished. You start the puzzle and it's going great! You get all the outside pieces with the straight edges put together. Then comes the heart of the puzzle, and boy is it tough now.
Don't give up, though, because it's going to be a beautiful thing to see when it's all put together. Sure, there may be times when it seems like there's no way you'll get it done, and that the puzzlemaker must have forgotten to put several pieces in the box. And just when you're at your lowest and ready to tear the puzzle apart, your puzzle-friends will stop by on the weekends and solve a couple of pieces and remind you how awesome that puzzle will be when you get it done.
Kinda like writing. Everyone wants to give up at some point. Heck, J.K. Rowling almost committed suicide at one point. (Literally.) But then your family and other writer friends sympathize and encourage you, and maybe even solve a piece or two of that puzzle, and you keep plodding forward. So stick with it, because that puzzle will be something to behold.