In our culture that so loves do-it-yourself, book publishing is becoming more do-it-yourself than ever. In so many ways, that's a good thing. You, as an author, can now be far more in control of both the process and the product than was possible, or even conceivable, not too many years ago.
So when it comes to your very own manuscript which you want the world to see and enjoy at once, why bother seeking help on it from a professional editor? Why commit the time and money?
Here are 5 random answers:
1. First, no one is a perfect writer or self-editor. You can be assured your manuscript has flaws that are invisible to you--places where the reader gets stalled or confused or bored, or strays from your intended meaning. As the author, you're simply too close to your manuscript to clearly see those. An editor's fresh, professional eyes can spot the vast majority of them and fix them, or help you fix them.
2. Your book isn't ultimately about you--it's about your readers. An editor's job is to be the advocate for your readers--and you owe that to them, for their sake.
3. Although your mother and all your best friends have pronounced your manuscript to be perfect just the way it is, the sad truth is that they simply can't be trusted on this. Only someone who doesn't know you can maintain the objectivity required to make the most of your manuscript.
4. In the grand scheme of things, the time it takes a good editor to process your manuscript is not really that long. Making your book better is well worth a delay of a few weeks, or a month or two at most.
5. The better your manuscript already is, the more likely a good editor can do what's necessary to help your book reach the upper echelons of high quality, long life, and lasting impact.