I originally published this piece earlier this week over at The Awl.

Just because an agent approaches you doesn't mean you have a good book idea.
The agent may have heard of you and figures that if you've written a million words online, you might be willing to publish 60,000 of them in a book. But the things you wrote might not make sense for a book. While the agent might love you and your voice, she might not be so hot on your other ideas, which can be confusing. Didn't the other ideas come from you and your voice?

Just because you write most of a book doesn't mean you can finish and sell a book.
Doesn't it seem like if you can do most of something, you should be able to finish it? Like, if you run 23 miles of a marathon, you can walk the last few miles. If you eat 3/4th of a pizza, you can cram in that last quarter. But you cannot, it turns out, walk the last three miles of your book.

Just because you write all of a book doesn't mean you can sell a book.
This seems strange, because people (including agents) have told you how great you and your voice are. Now you have a manuscript. Why aren't you rich yet?

The process of writing, editing, selling, editing and publishing a book is agonizingly slow, perhaps even slower for the blogger who is used to the immediate gratification of seeing work published immediately.
A book can take a full year (sometimes a year and a half) to be published after it's been sold. This can be hard to explain to your father, who wants to know why it takes so long and you realize you're not sure you know exactly, even though it's been explained to you. Incidentally, your father may have offered to publish your book himself if you couldn't sell it, which is heartbreakingly touching and frustrating at the same time.

Just because you wrote a book doesn't mean people want to buy the book.
Even if you tell every single person you have ever emailed about it. Even if you get out there and ask people nicely with pleading yet polite eyes.

Just because you wrote a book doesn't make you immune to comments like "How come I haven't heard of your book?" and "Does it bum you out that your book wasn't a bestseller?"
Even if you are murdering them with your eyes, you still have to say things like "I don't know, I guess it must not be very famous!" and "Well, yes, of course, but..."

Just because you wrote a book doesn't mean your editor will offer you a contract for future books.
This is especially tough if all your other writer friends have signed contracts for future books, and they complain about their deadlines for future books and you think, "I wish I had deadlines for future books."

Just because you wrote a book doesn't mean you are immune from bouts of jealousy regarding your more successful friends.
This is a hard envy to quash because unlike some other writing goals you may have set that were competition-induced, such as, say, publishing in a certain magazine or website, you'll realize that book publishing is less in your hands than other forms of writing, which should be a freeing thought, actually, but it's not. Fortunately most of your successful friends also have experienced this malaise and will talk to you about it over drinks.

Just because you wrote a book doesn't mean your editor is interested in your future books.
You can keep trying, though.

Just because you wrote a book doesn't mean other editors will be interested in your future books.
This could make you sad if you really liked your editor, just because you might feel like you let him or her down. It will also just make you sad because, you know, you wrote another book and you'd like it to be published and now you have to find a new editor. You think back to all the "shortcuts" you had with the first book (like an agent finding you) and realize that this process takes only slightly less time than evolution. On the upside, maybe you will grow a fin by time your next book is published.

Just because you wrote a book doesn't mean your agent will think all your future book ideas will be great.
But you need to keep trying. Even if you're wondering if you'll ever have a good idea again.

Just because you wrote a second book doesn't mean your agent will think it's great.
This seems disloyal somehow, even though it's just business. Shouldn't the agent be able to tell you a quick fix to take your book from unsellable to great? Like, maybe a font change?

Just because you wrote a book you don't become immune to the self-doubt and agonizingly slow pace of writing another book.
You're going to get mad at yourself and think, "I did this already. I should know how to do this! It should be easier this time!" You kick yourself for once joking that you hope it takes less than the ten years it took to publish your first book to publish your second book, because even if it does, nine years is still a really long time.

Just because you wrote a book you don't necessarily what you're going to do next.
You may jokingly say, "Maybe I should just go to law school" except that joke isn't funny because you would hate law school and you already know plenty of lawyers who hate their jobs and their lives. So you can't even stick the landing on a stupid self-pitying joke. Maybe you should just have a kid. Or keep trying to write. Or both.