You may think that you can sift through the bookstore, purchase a few screenwriting books, watch a few movies and then type out the next big flick to hit the theaters. Maybe you can, but I sincerely doubt it.
When you put together a model car, you follow directions and glue together the pieces but when you are through, do you understand the essence of the car? Do you understand the organism of a thousand parts working in unison after slapping on the last pin stripe decal?