It's a question every author asks himself after every session of writing. We are constant self-doubters. We second-guess everything we put to paper (well, most of us do. The rest, should).
The truth is, your writing is supposed to suck. At least during the rough draft phase. That's what rough drafts are for. That is why they are called 'rough' drafts. You sit down with pen and paper, or with your laptop propped in your lap underneath a tree, pouring every thought that runs through your head with no filter. If it pops into your pretty little head (reserved for the ladies), you commit it to the document. You don't discern good from bad. That's what the editing phase is for.
So, yes. In the beginning, your writing does suck. It's supposed to.
It's what you do after the rough draft phase that matters most. If you simply take your garbage, pick out a few maggots and send it out to the caterer, then in all likely hood the wedding party is going to vomit the moment they step up to the buffet line. Proofreading is not editing. Editing your work is just as important as writing it in the first place was, so if you don't take that seriously, your writing will still suck when you get it to your readers. They will most assuredly barf it back up. Some readers will be nice and if you're still in the free marketplace, you will likely get nice ratings, because readers in the free market pay you by giving you compliments. Even if they are overly generous. (You can still gauge your progress using sites like SOL. On SOL, for example, if your score remains below 8.00, you haven't brought your piece out of suckville. You have more work to do).
If your first round of editing doesn't have enough red ink to alarm you, then you've done it wrong. No matter how skilled a writer you believe yourself to be, massive amounts of red ink after that first round of editing is key to knowing you've taken your writing out from suckville and put it into the neighborhood of 'maybe I can stop sweating so much'.
You have to question every decision you've made. You have to put your analytical mind to work, questioning every word of dialog. You have to ask yourself if your characters are interesting enough, or if you ever bothered to bring them out of cardboard city. Did you develop some theme that you were previously unaware of? Do your scenes flow and compliment each other? Do your climactic points ebb and flow? Have your offered too little description, or did you go overboard to the point that your readers will skip pages? Are there scenes that should be cut and others added? Did you let a character live that needed to die a long time before? These are some of the questions you should ask yourself before going on to the next round of editing and you should have scribbles in your sidebars, giving yourself instructions, taking notes, sharpening your story.
Usually, during a first round of editing, I end up changing as much as twenty percent of my word count, deleting ten thousand words of text in a fifty-thousand-word story and adding ten-thousand new words. Better words (hopefully).
The second round of editing isn't so intensive but it is still serious. I focus more on flow and wording, making sure I am concise where I should be and elaborative only in the places where I can get away with it. It's where I kill most of my darlings; those cute little phrases I throw in just to try to sound smart. Those definitely have to go. I'm not there to sound smart. I'm there to tell a story.
Then there is the final round. This is the round where you focus on those commas and spelling blunders, where you toss your fishing line out, hooking those homophones and deciding if breaking the semicolon rule was such a good idea after all.
Only after this point, do you ever consider sending it to someone else for a second look.
Can you get away with skipping some or all of these steps? Sure. No author police will ever come knocking on your door with cuffs in their hands, but if you do skip these steps, you are only cheating yourself. I've learned much more about writing from editing my work than I have by doing anything else. When I write my rough drafts, my creative mind is in creative mode … not learning mode. When I edit, I am in a more logical place and my conscious mind is more involved. If you short-sell yourself by taking shortcuts in the editing mode, you will never reach your full potential as an author and your writing will ALWAYS suck.