For the most part, writing is not a group activity. Most writers write alone and sometimes even in their basements (not me, though). When you write your best friend is often your computer or laptop. I have two best friends -- a desktop and laptop. Human beings are social creatures. We need interaction with more than our daily digital date with our computers. We need to get out and meet people. Writing also is supposed to be done for other people to read (even though some writers hide their work), so even if all you're doing is showing a few friends, it's still an audience. By joining a writer's group you are getting out and showing other people your work. You are able to talk about the experience. You can share that experience and get feedback. You can get fresh perspectives and ideas. You can commiserate on the experience and the like-minded journey. As artists, we have a collective unconscious about the experience and why we do what we do. I personally enjoy discussing and talking shop about the thing I love the most -- writing.
If you're in the greater Sacramento area and would like to join a fantastic group, check out Writers Who Mean Business. Visit www.Meetup.com and search for Writers Who Mean Business. We meet on the last Thursday of the month.