That's not really true. A writer writes a script. A director tells the story on the big screen. I don't know how many times I've heard, especially on these forums, stuff like: Just get a good writer and a visual director, throw them together and it'll be a great movie. Because the writer will provide the story, and the director will provide the visuals. The best of both worlds. It's gonna be amazing. That is NOT how it works. A director has to be good at storytelling. You can have a great script and a subpar director and guess what? The movie won't be great. On the other hand you can have a subpar script, but a GREAT director, who pulls it off so greatly, that the movie ends up being very good.
As a director you're a storyteller from the very first moment, when you're in pre-production, to the very last, when you're working on that last edit which may or may not change the outcome of your movie.