You've written your book, packed it up lovingly, and sent it off (usually in bits and pieces, by request) as directed by some agent or editor. Then you sit back and wait...
And wait and wait and wait some more, while you hair grows gray, seasons change, and hope withers into despair. Okay, maybe it's not that long, but it certainly feels that way. (Important note: The time passes far more quickly when you're working on something new. And unless you've been specifically asked for an exclusive, you should be multiply submitting. Otherwise, you really will go gray before you get anything accomplished.
At last, the stars align, and you hear back from the agent/editor, sometimes in a letter, but often in the form of a phone call or an e-mail. The answer's not a blunt rejection, nor is it an open-armed offer of representation or a publishing contract. This time, it's what's often known as a "revise and resubmit" communication. This means, the agent or editor sees significant potential but doesn't feel the book is working in its present form. It also means a significant investment of time as the publishing pro explains what isn't working, makes suggestions, and offers to reread and reconsider the manuscript with revisions.
Most of the time, to the agent or editor's disappointment, the revisions never show up. (They're really hoping things will work out, considering how much time they've put it.) Sometimes, this is because the author misinterpreted the communication as a "nice" rejection. Other times, the author hopes a different pub. pro. might love the project as is. And on still other occasions, the author is insulted, offended, and stunned to hear suggestions that she never would have otherwise considered, so her knee-jerk reaction is resistance.
So how do you know when the agent/editor's suggestions are on the mark vs. when they're something that will gut your novel and turn it into someone else's?
At first, you really don't. Your natural instinct will be to defend your turf. My advice is to take careful notes if this information comes at you via phone. When the publishing pro stops speaking, regurgitate what they've said and ask if you have it right. Don't argue, ever, and don't try to explain. Simply thank the person for taking so much time and inviting you to resubmit with changes. Then say you'd like a little time to think about the requests. Or, if they immediately make sense to you and seem do-able, set a quick but realistic turn-around date by which you intend to have the manuscript back to the pro for consideration. Do not let seasons or years pass before replying.
It's easier if you receive the invitation and revision suggestions in writing. Then you can scream, shriek, and holler, "Are you kidding? What a freaking idiot!" to your heart's content. You can call your critique partners, too, for some wailing and kvetching... but lots of times, before you're through, it's going to start to sink in.
That agent or editor was right. At least about some of it. And the more you think about it, the more you'll realize, I can do this. Maybe I won't fix the problems in exactly the way she suggested --because by this time a better idea has come along -- but this book will actually be better with the changes.
That's when you know to go ahead and bite the bullet. Because the fact is, this agent/editor has a heck of a lot more experience than you do in the industry and a much more realistic and objective understanding of what sells. Chances are, you'll learn and grow immensely from working with this individual, whether or not you end up signing with her or selling to her.
Other times, however, the agent or editor is dead wrong. She's looking for an easy sale of whatever's hot at the moment, with no regard for your voice or storytelling sensibilities. She's attempting to mold you to a vision that's totally at odds with yours.
You'll know this is the case when, even after days of thought, you get a huge knot in your stomach and tears in your eyes whenever you contemplate some, if not all, of the changes. You don't see your book on the same shelf as this pub pro plans, and you know you wouldn't feel good about it even if her plan succeeded. Your critique partners or others familiar with the story are also flabbergasted by the requested changes (although your gut reaction should carry the most weight.) That's when you're right to say thanks, but no thanks. I don't see it that way.
None of us get crystal balls to help us predict the outcome of these decisions. All we can do is try to stay true to our own hearts and visions while remaining open to good sense.