If you want to be a writer, you have to write. You can't just think about writing or dream that someday you may put words down on paper. You also can't expect that you'll sit down and in three weeks you'll have the next great American novel. No, you have to write.
A Writer's Book of Days looks to create a writing habit. Writing needs to be done everyday, a regular writing appointment so to speak. Pen to paper. Write to write, not necessarily working on one particular piece but writing whatever happens to be on your mind, without editing or judgements. In the process, you will learn about how you write, your writing style, and what you have to say to the world.
A Writer's Book of Days is a wonderful resource for those dreaming of becoming a writer. It gives them a place to start and encourages them to practice and play with words. I think it also teaches them the important lesson that good writing comes in cycles and spurts.