In case you're not familiar with the process, here's how it works: You write a book. You revise it until it's good enough to publish. Then you find a literary agent, send a query letter introducing yourself and your book, maybe include a few sample chapters if that's what they ask for in their submission instructions, and you wait for them to respond. Ideally, the agent likes your query, asks to see the rest of the manuscript, likes the book, and agrees to represent you. Then the agent starts the process of trying to sell your book to a publisher. I've not yet gotten that to that point. So far this year I've received 48 rejection letters. The vast majority are form letters: "Thank you for submitting your query. Unfortunately, I'm not the right agent to represent your work, but the publishing industry is very subjective so keep trying!" Many agents let you know up front that if you don't hear back from them in X weeks, you should assume they aren't interested, so add to those 48 letters another 30-40 de facto rejections.
At any rate, rejection is just part of the game. If you are serious about getting published, you have to deal with rejection--lots of it. J.K. Rowling, Shannon Hale, virtually any published author will tell you stories of the numerous rejection letters they received before finding success. So as emotionally draining as this entire process is, the rejection also gives me a sense of accomplishment, like I'm paying my dues. I'm also doing my best to make it a learning experience, experimenting with different approaches and testing the waters with different books.
At the end of the day, I can't control whether agents will like my stuff and want to represent me. I can't control whether editors will want to publish my books, or whether readers will want to read them. All the things I can't control are kind of overwhelming, so instead I focus on the things I can control: I write regularly--admittedly September will be the first month this year that I hit my goal of 10 hours per week every week of the month, but I have hit the goal frequently throughout the year and even the weeks where I don't quite make it, I've written more than I would have without the goal. I submit queries regularly. I stay focused, which can be hard because the more you write the more writing ideas you have, but starting a hundred different new things without finishing anything does not get you published, so when those new ideas come I jot down notes, then get back to the project I'm working on.
Rejection is hard. Not having complete control over this thing that means so much to my sense of self is hard. Nonetheless, this year I feel better about myself--as a writer, and therefore as a person--than I ever have because I'm more focused on working toward this goal than I ever have been. I may or may not achieve my lifelong goal of becoming a published novelist, but I will live trying.