Every significant project represents the combined efforts of a team. Forget your romantic notions of the Solitary Author in their Garret. Technically, anyone can write a book with a pen and some paper, but every great book is a joint effort, even if one name nearly always graces the spine. The creative team on a book goes beyond the professional book collaboration I do today or the editing I did at publishing houses. Every successful author relies on other people. Even the "self"-published ones.
Team roles are amorphous. They depend on the art form, the genre, and the temperament of the originator—which is all any of us end up being. Originator, not Creator. An old colleague who reads a lot in your genre might be amazing at working out plot inconsistencies and helping weed out clichés. The presence of an old friend might establish the safe and supportive space you need to spitball ideas. And sure, you can seek out professional help with anything from historical research to copy-editing to just keeping your files organized.
If you're struggling with your writing, step back for a minute and look at the team you've assembled. Do you have the right people in the right positions? Seek help wherever you can get it.
In many cases, an author's spouse plays a role, as Véra Nabokov did with her husband, Vladimir Nabokov. Without Véra + Vlad, there would be no Speak, Memory, or Lolita. As Vlad's editor, translator, editor, and inspiration, Véra mattered to the final product. Whether her contribution was less, as, or more important than her husband's contribution may be relevant to students of Nabokov's work, but it's beside the point here, which is this: If you don't find a creative team and leverage the heck out of it, you're striking sparks with flint alone.
In part, amateurs shy away from the idea of collaborating with others, especially those with more experience in key areas, because of this false notion that pros do it alone. In my experience, some pros invest effort in disguising or minimizing the efforts of collaborators, and others cheerfully share credit. But they all have teams, and whether those teams are visible or not doesn't affect the audience's reception either way. However, the creators who insist we pay no attention to the wizard behind the curtain do a disservice to aspiring creators by implying that anything as complex and challenging as a great book, album, film, or work of visual art could ever be a purely solo endeavor.
(If you're already thinking of a great "solo" work as an exception to this, check its Wikipedia entry or iMDb page before you email me.)
The anxiety we experience around keeping Who Made This clear damages not only the creative process but also the audience. For example, the ludicrous "auteur" theory of filmmaking—a concept only a lazy critic could love—leads viewers to pin credit for something they enjoyed on one among many significant collaborators. This denigrates the contributions of the team and makes it more difficult to surface other worthy films.
George Lucas isn't the recipe for The Empire Strikes Back. You get Empire by mixing Lucas with screenwriter Lawrence Kasdan and producer Gary Kurtz (and others, of course). Subtract Kurtz's contributions on the third film—after he got tired of Lucas's prioritization of merchandise over movies—and it doesn't taste the same. Instead of Empire, you get Return of the Jedi. Instead of "No, I am your father," you get, "Yub Nub."
Giving all the credit to a single creator this way gaslights the audience, never a good idea: "I know something isn't right about this, but it's the same person. What happened to them?" Don't fool yourself. The greater your creative ambitions—and regardless of what you're making—the more you will benefit from a well-picked team of talented collaborators. Let each contributor play to their strengths, and watch that shack become a skyscraper. Sort out credit and bylines when you're finished. First, create something worth taking credit for.