Growing up, I wanted to be a fiction writer, but I feared I wasn't good enough. Then, after college, I worked for a magazine where I read fiction submissions. Most of the submissions were terrible, and I was curiously encouraged: if other people were willing to try and fail, I should be willing to try and fail, too.
I believe this is one of the most important lessons a writer can learn: You must always be willing to risk failure. Another lesson: Don't take rejection personally. So much is luck—finding the right editor at the right moment when he or she will be receptive to the story you've submitted. I know this first-hand. Both my novels were rejected many times before they found a publisher. The short story of mine that has done the best, that has been performed on "Selected Shorts" and anthologized in Spanish translation and cited for distinction in Best American Short Stories, was rejected by more journals—over forty—than any other short story I've written.
Each time you sit down at your computer you know it's possible that your novel won't pan out. Even when a novel does pan out, you never know how long it will take. My first novel, Swimming Across the Hudson, took me three years to complete; Matrimony took me ten.