How long would it take you to write a book? Maybe less time than you think. The first Sherlock Holmes novel, A Study in Scarlet, took only three weeks to write. So did Jack Kerouac's beat classic On the Road. And Irish novelist John Boyne claims he wrote The Boy in the Striped Pyjamas in less than three days.

Compared to those feats, four weeks seems like plenty of time to write a book. This month, half a million people all over the world are trying to do just that, in celebration of NaNoWriMo, or National Novel Writing Month, which takes place every November.

The rules are simple: Complete a 50,000-word manuscript (it doesn't have to be a novel) between November 1 and November 30. If you sign up at the NaNoWriMo site, you can be eligible for prizes and discounts if you complete the challenge.

I know, you're already too busy. We all are. Why should you even consider trying such a crazy thing? Here are a few good reasons you might:

1. It's the ultimate self-challenge.

If you've watched Matt Cutts's TED Talk "Try Something New for 30 Days," you're likely as intrigued as I am with the idea of giving yourself 30-day challenges. NaNoWriMo (which Cutts has done) is one of the more audacious challenges you can give yourself. I mean really, who can write a book in 30 days? If you do it, you'll be able to say, "I can!"

2. It's the next big thing.

NaNoWriMo has grown rapidly since it was launched in 1999. Last November, 431,626 people on six continents sat down to write 50,000 words in a month and about 40,000 of them actually did it. This year, organizers are expecting more than half a million participants, and there will be weekly "pep talks" from famous writers, prizes, and many other events all over the world related to the novel writing month.

3. You'll meet interesting new people.

Writing is generally a solitary pursuit, but not in November. There are NaNoWriMo events all over the place where people get together to write communally. There may be writing sprints, inspiring suggestions to get you going, presentations, and more taking place in bookstores, libraries, cafés, and bars in your community. It's a great way to get out and make new connections.

4. It will make you a better writer.

When people hear I'm a professional writer, many of them respond, saying something like: "I wish I could write," or "I find it so hard to write." Participating in NaNoWriMo will make you better at writing and also more comfortable just getting words down, which can be the most challenging part of it, especially if you're not an experienced writer. Get through 50,000 words in a month (or some portion of that) and suddenly writing a blog post every week won't seem daunting at all.

5. It will get you in touch with your passions.

Whatever you write, whether it's a novel or a nonfiction book, you should write something you feel passionate about. If you write something you think you "should" write, November will be the longest month of your life.

But whether you write about a story that fascinates you, or a topic you've always wanted to explore, or your own memories of a wonderful time in your life, or a terrible period you need to get off your chest, spending your time immersed in something that ignites your passion is a wonderful way to spend a month. And it can help you bring that passion back to your work and the rest of your life.

6. It will spark your creativity.

Writing 50,000 words, even if they're nonfiction, takes a lot of creativity. There's actually nothing like working with a constraint, such as a tight deadline (or the 140-character limit of a tweet), to bring out people's creative powers. And just in case you need further help, NaNoWriMo organizers hand out "plot bunnies," pieces of paper folded to (vaguely) resemble a rabbit's head with an instruction for something you need to write into your story. My husband is participating in NaNoWriMo along with a novelist friend, and received this plot bunny yesterday: "Your main character gets drunk and confesses something..."

7. It's better than brainstorming.

Love it or hate it, a key element of a classic brainstorming session is that there are no bad ideas. Writing 50,000 words in 30 days is similar, in that you'll be roadkill if you stop for too long--or at all--to worry about whether what you're writing is actually any good or not. Or if you go back and rewrite anything you've already written. "December is for editing," the saying goes among NaNoWriMo participants. Writing without worrying about whether what you've written is any good is a very freeing feeling.

8. You could actually wind up with a book.

I know, I know. But you would be far from the first. Hundreds of books that began as NaNoWriMo projects have wound up on bookstore shelves. Sara Gruen's Water for Elephants and Erin Morgenstern's The Night Circus are two huge bestsellers that emerged from the November novel-writing challenge. Who knows? Maybe that compelling story you've been wanting to tell will become the next big NaNoWriMo success.

Ready to join my husband and 500,000 other participants in NaNoWriMo? Let me know in the comments how it goes.