With a good script, a good director can produce a masterpiece. With the same script, a mediocre director can produce a passable film. But with a bad script even a good director can't possibly make a good film. For truly cinematic expression, the camera and microphone must be able to cross both fire and water. The script must be something that has the power to do this.
Kurosawa spent considerable time, sometimes years, creating storyboards for his films.