Hm. This is kind of a rambly response, sorry Wildbow, but it's your fault for being thought-provoking.
Criticism isn't fun, and even in the best of times it can act as "drag" that I have to fight against in order to keep momentum going. Palladian's critique of Curveball was necessary and useful since it highlighted something I've actively struggled with for a while (and it's proof that even when you're aware of problems and working to overcome them, that's not always enough to succeed) but even then it made me second-guess myself a lot and generated a whole lot of extra inertia that I had to fight through when I kept writing.
I wonder if frequency plays a part, there. When you get a steady stream of feedback, good and bad, on a project I suspect the bad isn't particularly fun but statistically speaking when you reach a certain point you're going to know a) how much to expect and b) where it's going to come from, and you can steel yourself for it and move on. When you don't have that level of success (nothing I do is on the level of Worm or LoN, for example) then any feedback at all is sort of like a flash going off in a pitch-black room, where you only get a brief image of wherever the flash went off. So a good review, you get a brief image of people partying and giving you a thumbs up, which is great. A negative review is a brief image of a Deep One rising out of the waters preparing to drag you down to the depths -- not so great, and then the flash goes out and you have images of the thousands of Deep Ones you didn't see silently bearing down on you.
For some reason I never get the image of thousands of revelers enjoying my work. Nope, it's just the Deep Ones. Damn you, Lovecraft.
The trick is to learn to go on in spite of this, which is not the same as having a thick skin. I don't believe I have a particularly thick skin--if I didn't care what anyone thought, I wouldn't bother putting it out there. I want people to enjoy my work and when they don't it bothers me. At the same time, I am possessed with a certain arrogance that I think is common in a lot of people in the arts: I have specific stories I want to tell, and I want THOSE STORIES to be the ones that people like. Art is kind of the ultimate version of trying to "have it all" because I have something specific in mind that I want people to love, even if it's not the something specific THEY have in mind when they go into it.
So here's an example:
Before I published Pay Me, Bug! as a web serial (it was a completed work before I serialized it) I had a particularly crushing moment when someone out of a review group went into detail about why the protagonist of the book (Grif) was a terrible character and had to be rewritten. I want to stress that this was not a particularly nasty critique -- it wasn't angry or sneering or cutting -- it was a very well-reasoned explanation of why the specific "type" of character Grif was didn't work for the reviewer, and why it damaged the story. And also keep in mind that this was the most detailed response I had from that group of reviewers -- other than this response, everyone else was rather tepid ("I liked it" and "I laughed" and "I thought it was fine" are not really informative).
So that criticism STUNG, because Grif was by far my favorite part of the entire book. The cheerful, amoral rogue is a personality I feel I write very well, and is an archetype that I tend to get behind and root for--I mean I practically imprinted on Han Solo when I was seven or eight, it's been horrible for my wife --so to have my most detailed critique of my work talk about how insufferable the character was, well that was hard to take, and I had to wrestle with it.
And what finally came out of that was:
1. The critiquer's lack of affection for the character was genuine.
2. Other people will probably share that lack of affection.
3. However--and this was an important sticking point--Grif was the guy I was writing about. It was his story. The book doesn't work without him in it.
So I decided that no, damn it all, I wasn't changing him up, because he was the story I wanted to tell in that book. So I steeled myself and kept Grif with the knowledge that there were people who would hate, hate, hate, hate, hate him.
Overall it was a very valuable experience because the critiquer wasn't wrong--that level of smart-assery in a protagonist won't appeal to some people, and that's all there is to it, and I needed to be aware of that--but actually deciding "well, I'm doing it anyway" was, I don't mind saying, terrifying. But that's the story I want to tell.
On a lesser note, one of the criticisms I DID expect from the outset and was prepared for was "This is pretty derivative" and "paint-by-numbers space opera" which are reviews I have received in various places. I can't fault anyone for saying that, because it's true. I love a certain style of space opera and Pay Me, Bug! is definitely a love letter to that era. But I absolutely do nothing new with that genre, and I can't fault the people who ding me for that, even though my plans involve continuing to do nothing new with that genre.
OK, so I'm still rambling, but this just sparked another thought -- it's easier for me to handle criticism when I'm comfortable and in command of my material. So, for example, the criticism about Pay Me, Bug! was crushing but I was able to make the decision to continue on as planned because I had a very firm grasp on what I was trying to do and how to do it. I would contrast that with Chris' review of the first few chapters of The Points Between on this site, which just about killed me (I'm not picking on Chris, seriously, there's nothing wrong or untoward in his review, it's just not the one I wanted, heh). And the reason it just about killed me is The Points Between is about ten thousand times harder for me to write. It is in a style and at a level that is fairly alien to me--I'm more comfortable with smartass pirates in a space opera heist novel with hyperintelligent talking bugs, or smartass villain-turned-superheroes in a murder mystery/conspiracy serial, than I am with a story about magic hiding inside the modern world in the guise of art. Neil Gaiman could pull this off, I'm still not sure I can, and it's terrifying to try. And it WILL fail for people. There's no way around that. But being confronted with failure on something you're not sure you're going to be able to pull off creates a lot more internal struggle than being confronted with someone who simply disagrees with a decision you made that you're absolutely certain about. One is unpleasant and disappointing, the other feeds the little voice that whispers "you're doing it wrong you're doing it wrong you're doing it wrong you're doing it wrong" that plays on an endless loop whenever you try to start typing.
Of course at the end of the day none of that really matters when it comes to actual critiques, reviews, and feedback. There's no hand-holding in the great big world, and when people are reviewing your work they're not acting as your shrink or your cheerleading squad -- on WFG (for example) they're trying to tell OTHER READERS how they reacted to the book, theoretically to help those readers make informed decisions. On Amazon they're (theoretically) trying to chip in to let prospective buyers know whether it's worth their money. And it doesn't matter, for example, how personally terrifying it is for me to write something. My personal journey isn't important, the output is. If it falls flat for a reviewer, the reviewer, if he or she is acting ethically, has a responsibility to tell other people that it did, and why, even if it makes me want to curl up into a ball. That's the entire point of reviewing. The writer has to figure out how to keep going, and for me it's a matter of digging deep and inching forward (sometimes it's pretty close to the literary equivalent of an inch -- ten or twenty words at a time) in the hopes that you get there.