From the first poem you show a friend or a teacher, to five-page editorial letter from an agent who might take you on if you get the novel right, to a TLS review of your twentieth book, as a writer you never stop getting feedback on your writing. I've talked before about the basic decision about accept-adapt-ignore. But sometimes even that isn't enough to stop you agonising about whether you should change something in your writing because of what someone's said. And I would suggest that who that Someone is, is part of the decision.
These days it would be very un-PC not to say that everyone's opinion of your writing is valid, and in one sense that's true. But the flipside of that is that no one's opinion is valid in any meaningful sense, unless you choose to accept its validity. It's not arrogant to decide that you don't need someone's opinion of your writing: it's part of being a writer. I've seen so many aspiring writers have their confidence - and therefore their writing - wrecked, sometimes permanently, by being in the wrong environment (and not just that one particular, cultishly vicious online group). Even in good groups I've seen writers ruin a piece by trying to write by writers'-circle-committee, or by believing the all-too-many critiquers who critique by the rule book. Some of that is lack of confidence in a critiquer who doesn't know good writing when they see it, so they look for boxes ticked. Some is lack of confidence or experience in the writer, who can't hear their own instincts, or doesn't trust them.
Having said that, here are some questions to ask yourself about that Someone, when you're trying to decide if you should accept what they say.
1) Are they too afraid they'll hurt you to be frank? Even some very discerning readers know how much it hurts to get feedback, so they don't really give it, and you're left with nothing to work with. It takes experience, or natural talent, to give feedback in ways which are rigorous but don't just trash the work.
2) Do they think that sensitivity is for wimps? "This is shit" is no more helpful as a critique than "This is wonderful". And it will probably damage your confidence more. As I was exploring in To The Point, it all works much better when two people's critique-styles are a good fit for each other.
3) Have they said, "It flows very well"? Every writing teacher knows that this is the mark of the inexperienced critiquer. It means precisely nothing.
4) If they're sounding very confident in telling you what's wrong, have a look at their own writing. Every group has members who know all the rules and know all about what agents don't like and readers won't buy. They are very rarely good writers, sometimes not even competent writers, and they critique by the rule-book because they don't know real writing when they see it. Unfortunately, their confidence is catching, and so the rules get promulgated far and wide, while the good writer's good answer, "It's not as simple as that", goes unheard.
5) Who is saying it? Someone you barely know, online? Someone who hasn't read the first ten chapters? Your longstanding trusted reader? A friend who reads a lot but doesn't write? A member of the writers' circle who's had a run of rejections for the kind of writing you also do? A writer you admire but who doesn't teach? Someone whose job is being a typical reader for your work (editor)? Someone who has power over your writing (teacher, editor, agent)? Any of these may be very useful, but it helps to know, in deciding what to do with what they say.
6) How precise are they in observing their own reactions to the story? Can they pin down the words which aren't right for the voice? The sentences they didn't believe that character would say? The scene which meant they didn't bother to go on reading? The key good craft is to learn Problem Finding, and that's what this is. This, really, is what you need most and should try hardest to find; this is what will make you a better writer.
7) What are they saying? Sometimes one person points out a flaw and you think "Doh! how did I miss that?" If that's true, you don't really need to go any further: just change it. If you're not sure, you need to separate out their reaction from a) the reasons they give for it, and then b) from any solution they offer.
8) How many other people are saying it? If most of the writers' circle or six different agents are all saying the same thing, the chances are that most readers you haven't asked yet would agree.
9) Do they read your kind of writing (genre, form, degree of literariness) a lot? Just because someone rarely reads the kind of thing you write doesn't disqualify them from talking usefully about yours; it can be salutary to discover that plenty of readers don't get or are bored by what you aspire to write. But all forms and genres have certain basic elements, and if your reader balks at the violence in your crime fiction, the science in your sci fi, or the amount of readerly work your literary novel asks of them, then you don't necessarily have to listen... though you may win a wider readership if you do.
10) If they've missed the point, is it because they're not experienced in reading this kind of novel, or because you're not making the point clearly enough for anyone (i.e. everyone) who doesn't already know what the point is?
11) Are they talking about what YOUR novel does, or about the kind of things they like to find in this kind of novel? Do they dislike it because their expectations were disappointed?
12) Can they separate out their tastes and pleasures - what kinds of character annoy them or what topics distress them - from their experience of your novel as a piece of storytelling?
13) Do they seem to have understood what your novel is trying to do? Can they talk about whether it's doing it well or not, separately from whether they're enjoying it?
14) Can they set aside what they would do, if they were writing this project, this scene, this sentence? If they talk about what they would do instead is it clear that they mean it purely as an illustration, not a solution? Might you want to solve it another way? Do they try to bully you into agreeing?
15) Are they diagnosing the disease from looking at the symptoms? There are many ailments that give you spots. Not all of them are measles, and each ailment needs a different treatment. And, just conceivably, your novel is a leopard anyway.
16) Is what they say something you can work from? There are lots of things we can say about a novel which are entirely true and not at all helpful. On the other hand some people have a gift for saying the one thing - perhaps quite vague - which unlocks the door for you.
I do want to say, though, that any or all of these are at risk of being get-out clauses, so that you can fend off feedback altogether and end up changing nothing more than a couple of commas. Indeed, if your resistance is extra-fierce, I'd suggest that it may be because you're hearing stuff that you know in your heart is true, but don't want to believe. And if you find a critique partner who can say the stuff you don't want to believe, in a way which makes you able to tackle it, then grapple them to the heart of your writers' circle, and don't let go.