It is easy to assume that if you have good quality writing skills and are confident in your abilities, you will be able to edit your own work to a high standard.
For the vast majority of writers, however both novice and established this simply isn’t the case. Yes, you may be able to read over your work and correct basic errors, but are you picking up every single spelling mistake, plot hole and questionable use of grammar in your beloved manuscript?
The answer is usually a resounding no. Even the best author in the world needs help with proofreading and manuscript editing, and the main reason is this: writers get too close to their projects. They work on them for weeks, months, sometimes years, and in that time they’re likely to read their words hundreds and thousands of times over.
Taking a break from the manuscript and coming back to it with fresh eyes may work in picking up a couple of obvious mistakes, but fresh eyes are always freshest when they’re someone elses.
Giving your work over for critique can be hard, but a proofreader will be able to bring a much-needed new perspective to your manuscript. Having not heard about your story or novel before and having no preconceived notions about you as a person is a huge advantage; if you ask a friend to proofread, they will probably (whether subconsciously or not) go easy on you and be more likely to praise rather than criticise. Professionals can only go on what is written on the page.
Not only that, but expert editors and proofreaders are extremely well versed and up to date with grammar usage and writing conventions that you may not even be aware of. This gives your work a professional feel that you simply may not have been able to achieve on your own, and also gives you the peace of mind to present your finished work without any niggling doubts as to its quality.