It is a truth [that should be] universally acknowledged, that an author in possession of a finished book, must be in want of an editor.

All writers engage in self-editing, whether we edit as we go along, in bits and pieces, or systematically after a draft is complete. It’s a natural part of the writing process: clarifying a few things here, adding some color there, and cajoling our book into what we hope will be the final draft.

The next step is not always clear. Do I write a proposal and pitch to an agent? Do I forge ahead to self-publication? These are important questions, certainly, but they leapfrog yet another important question that many authors fail to consider: Should I hire an editor?

Although writers and editors are kindred spirits, they fulfill fundamentally different purposes for a book. Where the writer imagines and creates, the editor interprets and refines. To do both well in a vacuum is hard enough; to do both well on the same book (especially one you’ve written yourself) is nigh unto impossible.

The best editors are well-trained, with experience and judgment that enable them to honor your intent, style, and voice while suggesting improvements and changes that better connect your story and your readers. Peruse the acknowledgments of any book on your shelf, and you’re likely to read some glowing thanks to the army of editors who helped the author develop, correct, and polish their work.

Of course, editing requires an investment of both time and money, which may not always be within reach. But for those who are debating whether an editor is necessary or helpful, consider these reasons why it’s so difficult to edit your own book.

You might not know as much about book editing as you think.

For a confident writer, it’s pretty easy to read a sentence and correct it for punctuation, grammar, or spelling. Most writers instinctively self-edit as they go, and some writers may even have professional experience editing client projects, white papers, blogs, essays, digital content, or newspapers.

But book editing is an entirely different creature. For one thing, the sheer size and scope of a book makes having that macro view really challenging, especially when you’ve been living inside that book for many weeks, months, or even years. For another, there are different kinds of editing. Copyediting, for example, takes care of grammar, spelling, punctuation, and small details, whereas developmental editing considers big-picture issues like structure, pacing, characterization, plot, and language.

It’s not enough to have great writing skills; a good editor must know how to make a book better by identifying and correcting problems that might distract a reader. Like writing, editing is an iterative process, and professional editors usually end up specializing and working together to fully polish a book.

You’re too close to the work.

Working with an editor is invaluable because of their objectivity. Many of us writers pour our hearts and souls into our work, and that means we have little or no distance to evaluate it.

“As you compose and craft, like any good parent does with a child, you don’t see your work for what it is,” writes Jeff Goins in Why Writers Can’t Edit Their Own Wrok. “You see it for its potential, for what you imagine it to be. In other words, you’re blind to reality. To the fact that you left out a word (or several), missed a comma here, and so forth. You need some fresh perspective. You need someone you trust, someone to speak the truth in love and help make you (and your work) better. Not anyone can do this. But someone should.”

You’re too critical about your own writing.

I once had a college instructor who informed my creative writing class that none of us would get an A. In fact, a B+ would be our greatest aspiration, because he didn’t believe in perfect writing. “It can always be better,” he said.

This way of thinking can drive perfectionist tendencies. Suddenly what might have been good enough gets reworked over and over. You might berate yourself, or explain to others just how terrible your writing is with little to no regard for its merits. This approach destroys spontaneity, your original creative instincts, and your appreciation for your own craft. More importantly, it’s one of the best ways to hate the act of writing. If you land anywhere on this spectrum, you should never edit your own work because there’s a good chance you’ll never be content with it, and you’ll find yourself holding on to your book for years, never permitting it to see the light of day (or the eyes of readers who’ll love it).

“The struggle between ‘I’m the greatest writer who’s ever lived’ and ‘This is drivel; I should quit writing’ is real,” writes Blake Atwood in You Can’t Edit Your Own Book and Here are 7 Reasons Why. “But take heart: if even Steinbeck doubted himself during the writing of arguably his best novel, East of Eden, then it’s OK to be wary of your ability. When you’re insecure about your book, you won’t know what needs to be kept and what needs to be discarded.Instead of thinking every word, scene and chapter are astounding, you’ll mistakenly believe that they’re all rubbish. Neither belief is true.”

You’re not critical enough.

The other side of the “too critical” coin is feeling so confident in your own abilities that you dismiss the very real help an editor can provide to your work and your craft.

“If you’ve ever typed The End with a flourish and then hit Send immediately after, you’re guilty of writer’s hubris,” says Atwood, adding that while it’s important to celebrate completion of one stage of book creation, it’s important to recognize your journey to publishing is far from over. “Overconfidence leads to believing your book needs far fewer edits than it deserves.”

You don’t have fresh eyes.

You know what you’re trying to say, so your brain might instinctively hop over missing words or accept awkward phrasing. Most authors go through many revisions, and sometimes in the process you can introduce errors with characters, descriptions, and even major plot points.

“The culprit here is confirmation bias,” explains Crystal Jepsen in This Is Why You Suck At Editing Your Own Writing. “Confirmation bias is the tendency to search for, interpret, focus on and remember information in a way that confirms one’s preconceptions. When you are self-editing, your mind is filling in the blanks and auto-correcting errors that you end up missing and not actually correcting them.”

To work around this if you’re in a pinch (or short on cash), either read aloud your own work, have someone read it to you, or have your computer read it aloud in its charming monotone. “The best part about using a computer to read it is the computer has no emotion, so it’s extra fun to listen to it read your work to you,” Jepsen says.