There seems to be two camps on this issue: share your early work with those in your critique group, or hide it until it makes more sense so you're not embarrassed or swayed by others' opinions. I've always been pretty much in the "rip my chest open and let the bleeding begin" camp.

Usually I plot out my story in its barest form all the way through to the end, and then write to fit that skeleton, ready to change things if a better twist comes to me. When I share my early work with others, while I've invested quite a bit of time in plotting and figuring out the basic personalities/strengths/goals of the characters, I haven't spent all that much time being "with" my characters yet. So when I start writing the first draft, it's like any new relationship I've been in––it takes awhile to get to know the person, to appreciate their hidden talents. And perhaps observing what behaviors aren't so great.
Although I'm sometimes (okay, often) embarrassed to hear comments that point out gaping holes in my storyline or polite remarks on dreadful character traits that somehow I missed, those suggestions are always therapeutic. If my critique partner explains that my MC is a spoiled brat who they hope fails miserably and was this what I wanted?, I need to change her––FAST! And I do. I imagine meeting this person in real life, and try to alter her so that she still fits my vision of the story, but is compelling to readers at the same time.
If, on the other hand, I've waited until I've written the entire first draft to share, I worry that I'd be too invested in my characters and plot to want to change much. Like bringing out my newborn for people to admire, only to have them point out the flaws. I imagine that it would be more difficult to want to make sweeping changes that would resonate throughout the whole story (and maybe feel a little sad that my newborn isn't as cute and cuddly as I had hoped).
Your turn: Do you share your novel while it's still a sparkle in your eye, or wait until you've given birth to the newest member of your writing family? I'm sure there are pros and cons to both, and I'd love to hear how you work.

