The road to publication is narrow, winding, and long, and it begins with that little one-page distillation of what you want to write, your qualifications to do so, and why someone should represent you or publish the work. So much hinges on this document, the query, yet there's not a good way around it. Literary agent Nathan Bransford addresses this in an excellent post. One of the points that Nathan makes is profound: "Success is not the default." It's tough to get published, and once that goal is achieved, it's sometimes even tougher to repeat.
Another literary agent, Jessica Faust, has addressed how an author's behavior may affect a publisher's willingness to give a contract for a second and third book. This is especially problematic in light of today's economy. If you don't mind some of Jessica's rather direct language, you'll find this post interesting and (if you're a writer) instructive.
Is there a point to this? Yes, and it's those words of Nathan's. Success is not the default position. Everyone who sets out to write a book won't succeed. But every positive step taken along the way should be celebrated, because it sets you above all those who never even tried. Development of a concept, putting the words down, editing them, re-editing, writing the dreaded synopsis, crafting a killer query letter, pouring your heart into a proposal, trying time after time to win the favor of an agent, reading replies from editors that "this isn't right for us." Every time you go through a step, you've accomplished something. You've matured. You've changed. You've moved ahead.
If you're an aspiring writer, I hope you'll take heart and be encouraged. If you're published, I trust you're continuing to strive for improvement in your next work. And if you just enjoy reading, I hope you appreciate what it took for those words to appear on the page. It was a long road. And success was not the default position.