The short story and the novel differ in many ways, but the most important consideration is the time commitment involved. While it's relatively uncommon for a writer to work consistently on a short story for years, the average novel takes 3-7 years to complete. If you're going to commit that much of your life to a project, you want to be sure your novel idea is a good one. So how do you know if your idea is novel-worthy? A few questions will help you decide.
Does Something Happen?
It may sound simplistic, but for many people, the plot is one of the hardest elements to grasp. Make sure that your story contains a central conflict. Something must happen to turn your character's life upside down, and through this experience, a change must take place within your character. If your idea does not include a conflict, you're not quite ready to start writing. However, if you are passionate about your idea, and feel that you can follow it through until a plot reveals itself organically, then take the leap and start writing!
Will It Appeal to Others?
If you're reading this article, you probably do care about your audience. You probably hope to publish your work someday. If this is your goal, and you're going to spend 3-7 years on a project, do give some consideration as to whether or not your work will be of interest to others. Is it overly focused on you and your concerns? How does your theme apply to others? What will your reader gain from reading your book?
Are You Taking a Risk?
While you must consider your audience, don't be afraid to write something risky or outside the mainstream. Denis Johnson keeps a sign over his office door that reads, "Write the unpublishable...and then publish it." This rule has obviously worked for him, and odds are it will work for others. Ultimately editors and agents are interested in seeing something new. That won't happen if we're intent on writing only what we know can be published.
Is Your Novel Idea Compelling to You?
The most important person you have to sell on your idea is yourself. If your attention flags halfway through writing the book, your readers will pick up on it. Unless you're James Joyce, no one's going to spend as much time with your novel as you will. It's important to see your book through so that you gain confidence in yourself as a writer, but you want to enjoy the process. Writing a novel should be fun, at least some of the time.
That said, there is nothing wrong with knowing when to let a novel go. Many writers have many unpublished manuscripts. Remember: no time writing is a waste. You had to write what you did to get where you are (or where you are going). In other words: you couldn't have written the novel you published without writing (and not publishing) the one that you put to the side.
Are You Too Rigid in Your Outline?
Although outlines work for many writers (and can be especially helpful when writing a novel) be sure that you do not inhibit your creative process by adhering to it too strictly. If you find that you have new ideas while writing, then let yourself write them. Don't lose momentum by going back to your original idea.
Much of the process happens while you are writing, and it is important that you give yourself the freedom to explore all aspects of your story.