In the many posts I've done on the Realities of Self-Editing—yes, it's professional to edit yourself, and yes, it's possible (but not easy) to edit yourself adequately if you follow the secret—I haven't really addressed if you should self-edit.
Sure, I've said you should learn what goes into self-editing, so you can recognize a good editor when you see one, but…
Should you self-edit?
Short answer: Yes.
Long answer: It depends on what you're doing.
For a lot of folks, "self-editing" = a trap, because they get stuck in it while in progress on a story. There's a reason for the term "rough draft", and there's a lot of truth to the saying "You can't fix what isn't on paper."
Some of us actually have to edit as we go, else we get stuck, so it actually takes us less time to clean up that rough section than it does to try to force rough words on paper, but…
Folks like me are the exception, not the norm—and even I've learned how to sit down and force a thousand or three words out, then clean them up before moving on. (And I do have to clean 'em up before moving on, else I get stuck, but I've learned that because I've tried both ways more than once and timed it.)
Another factor in self-editing: What's the next stage for your story? If you're writing something as an experiment, where you're not even sure the bones are in place… If you can find a beta reader who can overlook the grammar to check if the story works, by all means, use them before you spend time editing scenes that don't work!
If you're behind or coming up on a deadline, and your agent or editor or whatever needs to see something—that's another situation where it might be best just to hand them the bare bones before you self-edit, but…that depends on how sensitive they are to grammar errors.
Some folks are so sensitive to grammar errors that, if there are too many, we struggle to see the story beneath. Line editors, copyeditors, and proofreaders are particularly susceptible to this, because paying attention to grammar errors is our job. We're trained to see errors, and turning that training "off" to enjoy a story for the story isn't easy.
So even if hire an editor to check the grammar on your work, you should try to edit it first.
So the editor can focus on fixing the errors you don't see.
Think about it. Maybe you know the difference between "break petal" and "brake pedal", but that doesn't mean you'll see it in your own work. (That one was found in Destiny's Kiss.)
If your story's full of grammar errors you could easily fix, that makes it harder for the editor to see the other problems, like the "break petal"s, so you won't get as good an edit—or learn as much—as you would've gotten otherwise. (You'll also probably pay more.)
Note that I'm not saying "Work your butt off to get a 'perfect' manuscript before you hire an editor!"*
Frankly, hiring an outside editor is something that even folks who can adequately self-edit do, because it's convenient. Don't underestimate the power of convenience.
If you can't afford to pay for editing, or if the convenience isn't worth what you'd have to sacrifice from your budget, don't underestimate the power of bartering or of beta readers, either.
But even if you do all your own content editing, line editing, proofreading…at least get another set of eyes on your manuscript in the form of beta readers. Don't post your book for sale and let those readers as your editors. They paid you for the right to enjoy your book, so as much as you can, give them a book that's enjoyable.
Readers who pay you are your clients. Show them the respect of offering them the best book you can produce.
Just remember: No book's perfect. So don't make yourself sick stressing over every little comma. Just do the best you can.
And take the things you've learned in writing that previous story and write the next one.
Do you have any more thoughts to add about self-editing? Do you have any other topics you'd like to see me address (about self-editing or other things)?
*Note: You do want to have a fairly clean manuscript before seeking a publisher, though, because it's unlikely that your manuscript is so great that they'll look past the unprofessional presentation—and to assume they'll edit a manuscript you submit on spec is unprofessional. ("On spec" means you submit the completed manuscript to ask them to buy it; if you've already a contract in place and have a grammar editor lined up, you can be less worried about it, but you still want to leave a good impression.)
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