I have found that being spontaneous or posting excerpts (and other things, for that matter) in the heat of the moment rarely work in the World of Writing. Or anywhere, now that I think of it. A very wise writing professor I had last semester said that you hold a huge amount of power in the moments before you click the SEND key...and that you need to carefully consider your next actions. So whether it be for a forum, an email (to friends, agents, or publishers), or on your phone, consider whether or not you are giving your 100% BEST for what you are about to share. It's always a good idea to sit back and give it a few hours, and in this case, it shows the rest of us who want to help that you have very carefully considered the advice that we have carefully given you.
I've said it before and I'll say it again: Don't give up. And if you do give up, don't wallow in your sorrows, for goodness' sake! Channel your frustration into learning the craft, or something else that makes you happy.
Best wishes
ETA: Elodie said: "...I chop and change chapters until I don't think it could be any better." To borrow from Joan Rivers' fabulous performance in the Geico commerical, I will add that my WIP has seen more chops than a Bennie Hana