I love helping people with their stories and pushing them to be the best they can be. And sometimes, that requires huge changes.
Behind the scenes with the other mentors from the Pitch Wars contest, I'm seeing plenty of discussion on what our place is in guiding our mentees to reach that personal best. Some people want their mentees to make huge content changes, like reducing the number of point-of-view characters, changing a book from third person to first, or drastically changing a plot line. And I think it's amazing that they would peer into a book and be able to come out with "I think your book would be better, overall, if you did this."
As a mentor far more comfortable with micromanaging (haha--I mostly just pick on language and do line edits), I don't think I would ever be able to suggest a massive overhaul like that, and for me, I've had the most success with author-led critique. I don't really want to tell them what story to tell; I want to help them execute whatever story it is that called to them. On occasion, I've gone as far as questioning whether someone needed to change POV or pull in more depth for a novel, but I've never laid down any ultimatums. I've never said "Your book has this central flaw, and until or unless you believe me that it must change, you will not succeed with agents or publishers." (As far as I know none of my fellow mentors are framing their radical suggestions in such a way, but I know it happens.)
I think part of the reason I could never go there is that it's been done to me.
You won't succeed unless this book has some sex in it.
You need to transplant the character from college into boarding school because college doesn't sell.
You need to make the protagonist older if you want her age to match her tone.
You can't write fantasy set in modern times. People just won't read that.
(These are paraphrases from people weighing in on my work in a professional capacity, meaning they're from editors, agents, or contest judges.)
But I wasn't resisting that criticism because of some belief that it couldn't help me. (Well, except for the last one. Obviously fantasy is successful in modern times in plenty of books.) I scrapped the criticism because I thought it was based on its author having a different vision for the story I wanted to tell than I did, and if I thought making their requested changes would harm the soul of the story, I didn't want to do it.
However, I've taken plenty of other criticism over the years. I reduced my word count--painfully--by more than 30,000 words because an agent wanted me to, and because I knew that could make it tighter and solve some pacing issues, I took her advice. She signed me. The first version of this story portrayed the main character as having no real social relationships at all, and a reader said that made her very hard to relate to--that even if I didn't want to give her friends, at least give her a pet she could be shown loving or something. I adapted that criticism and in the later versions of the book the protagonist had confidants in her study partners, though there was still some necessary distance in their relationship. I think it's a stronger story. I listened to what people said, and if I could imagine executing the story their way and still loving it for the same reasons I wrote it, it was worth a try.
Remember that even when someone you respect gives you advice, you can still respect them and believe they're off-base. Remember that multiple people might tell you something's wrong with your book but it doesn't mean you have to fix it in the way they tell you to. Remember it's still your story, and what you do with it is up to you. Take advice and criticism from your mentors seriously, but do not accept them as marching orders. They may be more experienced than you are but they know how to find success their way. If you can find it in your heart to give their advice a chance, do it, but if you can't, don't break your own heart. That isn't why we go into this storytelling business. There are tons of harsh realities in this line of work and yes, you'll have to get used to them, but not every person who talks to you about your work is objectively right about it.
Well, unless it's me and I tell you you have typos. ^___^