Yesterday I participated in an interesting discussion on Wattpad, started by an aspiring writer reluctant to show his work to agents and publishers out of fear of harsh criticism. I thought I'd write a bit more about this here.
First off, if you garner any personal response at all from agents and publishers, you can congratulate yourself on at least grabbing someone's attention. From my experience, most commonly you'll receive lots and lots of silence and some impersonal rejection notes.
If someone does take the trouble to point out flaws in your work, even if you disagree with their opinion, reply in a polite, courteous manner and thank them for their time and attention (unless, of course, we're dealing with " constructive criticism" along the lines of, "this is complete rubbish. You should give up writing altogether"). Also, even if your critic is rude, sit down and think if maybe, just maybe, there's a grain of truth in what they are saying. For example, if someone says, "I couldn't get past the first pages. They are filled with excruciatingly boring, meaningless detail", of course it will make you bristle. But is it actually true? Be honest. Maybe your opening chapter can, in fact, benefit from some trimming down of details.
Finally, if you want to put yourself out there, either via traditional publishing or self-publishing, you absolutely must NOT let criticism get to you. There will always be people who dislike your writing and even you, personally (yes, even though they don't know you, personally). I can testify to having actually received death threats (yep) in response to several items I posted online. You must develop a thick skin, if you want to go public and live to tell the tale.
That is not to say you ought to ignore feedback altogether and say that your work is perfect and the product of a genius, etc. But you just cannot afford to topple over every rejection letter or scathing review, taking them personally and letting them get you down.
Look at the big picture. View your work with a critical eye, with honesty and good sense. And just always keep writing, reading and improving; always strive to make the most of your abilities.