Daily Science Fiction (a fantastic sci-fi flash fiction magazine delivered to your e-mail inbox each morning -- I highly recommend subscribing if you like sci-fi). There's a funny phenomenon that I have realized occurs for me, at least, when your story is delivered to its public forum.
Suddenly any flaw in the writing stands in stark relief, to an exent it didn't on the computer monitor or even printed on the page and being red-penned. No matter how critical I can be of my own work in creation, it has nothing on how critical I feel of it when there's no more opportunity to alter it.
Don't get me wrong; I believe in that story, and I believe it had to be good for DSF to publish it. I love the stories they select, and therefore have a lot of faith in the editors - and their decisions. When my insecurities set in I took a deep breath and told myself to stop being a nutcase. I always feel this way about my work in print, which is pretty terrifying when I think about these entire novels I write and hope to publish (and also, reason no. 1 why self-publishing doesn't seem like a good option for me, personally).
We writers are funny people. Self-confident enough to create and share our own worlds, but sometimes with our own hang-ups along the way.
(And, if you're curious, you can read my short story, Ten Speeds at the End of the World, here)
6 hours ago