You have mail, and you can't resist clicking that little icon. Your heart stops. You breathe out. It's from an agent--or it's from your agent, or a small press. This could be the one. But it's not. And you feel like sticking your head through your computer screen. I get it. This is #67 and that book is perfect. There is nothing more you could do to it. Right now. With your current skillset and point of view, there is nothing more you can do to it. In a year, you may feel differently. You probably will feel differently. Especially, if you spend the next twelve months writing other stuff, adding thousands of words of experince to your bank.
It's hard to see now. You've spent months or years of your life working on something. You've got up at four am after going to bed at midnight to finish this and no one appreciates your blood, sweat, and tears. But being allowed to--or even forced--to keep your baby isn't always a bad thing. When you traditionally publish something, you're basically putting that baby up for adoption. It's not yours to protect and provide for anynore, but it's still your creation. You want it to succeed and have no control over what happens outside of your home. Self publishing does allow you more control, but self publishing something before your read still splashes your name, the only thing a writer really has, across a subpar product for readers to remember.
So the next time you get a rejection letter, delete it. Don't make a decision about what to do with the project right away and breathe a sigh of relief. You're keeping your baby another day. Think carefully and critically about acceptance letters. What's in the contract? What kind of marketing and editorial support can the press offer? Baby needs a good home, because once it's placed, it's placed.