Can you be your own editor?

On SheWrites.com, Heather Jacks has a useful post on editing:  Among her six tips for independent/self-published authors, she has this explanation of various editing functions, and why you need an appropriate editor for your book.
Here is a brief excerpt:

"There are a few types of editors. There are copyeditors, who will fix typos, misspellings, grammar, clean up your prose, and correct a fact; there are line editors, who will help you arrange your paragraphs; and then there is a most important type of editor, which I call a ‘planning editor’—that person who will partner with you on the project and tell you things you don’t want to hear, like you need to get rid of half of what you wrote or this isn’t a topic that warrants an entire book or this should be a screenplay, not a novel."