Getting comments and critique on your work is one of the most valuable ways to improve it. It's also something that you will have to deal with if you're planning on working with agents and editors. Finding the right balance between doing what's asked of you and putting your foot down is tough, especially when it could mean killing a deal (always a matter of last resort). There are two main questions you have to ask yourself when you look at a suggestion.
1, does is make the story better? If the answer to this is yes, you move on to question two. If it's no, you have to take a moment and think about why the suggestion was made (okay, so you should do that if it's a yes too, because you've just been offered a chance to learn something). I was going to talk about this in brief below, but I've discovered that it wants to be its own post on rewrites, so more on that later.
2, and potentially much harder to answer, does it advance the purpose of the story? This is the place where things go foggy and vary wildly depending on what sort of writer you are. If you've got the whole story in your head or in an outline and someone makes a good suggestion that doesn't follow along, you're posed with an immediate dilemma, go with the shiny new thing or stick to your outline. I've done both depending on the situation.
My very first short story sale involved taking the second half of a 6,000 word short and throwing it away to write a new ending. I've also looked at a beautiful idea and quietly (and somewhat sadly) put it aside. One of the few times I've really gotten hammered by a member of one of my writers groups (and rightfully so) was when I let myself slip and say that I wasn't going to do something at the time it was suggested. I had good intentions, but it was a breach of etiquette and absolutely the wrong way to handle the choice.
In general, if you're not going to take a suggestion, there's no reason whatsoever to tell the person who made it because it will only make them feel as though they've wasted effort. There are two exceptions to this. A, editorial/agent suggestions, in which case you discuss the problem the suggestion addresses and try to work out a comprise (more on this in the rewrite post). B, book length works where this person will be critiquing on an ongoing basis and where not taking the suggestion will have a significant impact on the reading of the story.
That latter was the case in the scene wherein I got hammered. I handled it the wrong way. What I should have done was shut my mouth and given myself a couple of days to think about it. Then, if I decided it still mattered (it would have in this case) I should have waited for the next meeting and spoken with the critiquer on an individual basis about why the (genuinely excellent suggestion) was incompatible with the novel I was writing.
What they wanted me to do would have made a good story, but it was a story that I had no interest in telling. The only way to stay sane in this business is to write what you love and love what you write. You are the one who is writing it and you are the one who's name goes on the byline--it has to be something you believe. You have to own the story.
So, does anyone have any thoughts on owning your work? Stories of critiques you loved but couldn't take? Critiques you later wished you had taken?