Unless, of course you want to.
But, to me, as long as you're enjoying the writing, the creating, the process. You're making progress. Keep on keeping on.
Actually, the venerable Miss Snark's First Victim, had a great post about quitting or not quitting back on April 5. Check it out here.
I've also blogged not so famously on Literary Rambles about not throwing in the towel...
Not that we haven't all thought about it once or twice.