We tell stories from the time we can speak. When we become articulate, we all start off telling stories about our lives in the first person. Eventually, we tell our parents and teachers and friends things in another mode, where we're mainly describing things that other people did. Then we become more empathetic, and speculate about why people did those things, what everyone was feeling. You could probably do a mapping of how we tell stories to Maslow's hierarchy, if you were inclined to do that.
The progression is the same for every writer. The first impulse when writing a story is to speak from the self. If we're not doing that, we're emulating some storybook voice we've learned. Either way, it's either too truthful or too falseful. Soon, we develop a sort of “writing persona”—an “I” which is a bit different from who we actually are. It never occurs to many writers to go beyond that. From the standpoint of craft, it's all that's needed to speak with authority on various topics, to give personal accounts, to narrate events, or to imitate the voice of a character doing any combination of those things.
You only have to browse Medium.com to see that the first-person mode is a sign of our times. Everyone has their individual voice to work with. Many expressions online may not be intended to endure, but the ones that aspire to the level of lasting, artful essays should employ a wider range of techniques. The reality is that readers enjoy a layer of formality between them and the authors they read. This layer is the result of a lot of difficult work on the part of the writer, in learning the tools of his/her craft. For more on what that means, exactly, check out David Orr's book on poetry, called Beautiful & Pointless. He has a wonderful section that delves into the complexity of craft as it's applied to deeply personal writing. He uses several great examples to illustrate the layer of artifice that always separates reader from author, and the difference that craft makes in first-person writing.
The fact is, when learning craft, writers need to learn as quickly as possible to get past the first person. By “get past,” I don't mean abandon it for good, or even for a short time. I mean it only in the sense of craft. It's very easy, with the proliferation of outlets for one's voice, to simply settle into it, to just speak as oneself and only slightly modulate it in order to form that authorial persona, or perhaps the voice of a character loosely based on oneself, all in first person. But there are many things that a writer can never learn until they learn them from working in the third person. They are useful techniques, and every writer should learn them, and learn them well, in order to bring them back to bear on their work in the first person.
Even a writer who is resourceful enough to create a first-person voice that is unreliable, interesting in its idiosyncrasy, unusual in its outlook, and entirely fictional, must get past it if that's the only voice they've ever written in. The punctum in such a voice is always the force of personality driving the character's narrative. The reader has nowhere else to go, and it's rare that a single voice will captivate all readers and sustain that captivation for the length of the narrative. What's more common is that there is some detail, some foible, that strikes us along the way, throws us off—even if it's absolutely true—and that will be the undoing of the work. Even if that thing comes from the writer's heart, or from the absolute center of believability in the character, it can throw us out, as John Gardner said “of the dream.” Often the avoidance of those foibles depends on a deeper knowledge of how narrative works.
To move to the third person, and to realize that accomplishing certain feats in the first person requires it, is a difficult goal to instinctively see. What—a writer will ask—are these things we will need to learn, which may only be learned by working in the third person?
It's a good question best not asked. Sometimes its answers, or “object lessons,” can interfere with one's unique approach to writing. But if we have to boil it down, I would summarize it as degrees of distance. It's the various narrative nuances within broader categories such as “close third” or “omniscient.” The power of it for storytelling is simply the ability to place the reader into the minds of different characters, or into the mind of the world. Once one learns how to do these things, they can also, amazingly, be done in first person, but not without first understanding how they work.
If there were only one single book I could recommend to writers who want to begin a study the nuts and bolts of this, it would be Anna Karenina. I'm not personally a fan of Tolstoy’s work compared to other authors of his era, but his technique is unparalleled and extremely polished. As one of those “object lessons,” the book is very useful. At one point, his omniscient narrator slips into the mind of a dog, with convincing results. (Hemingway did a similar thing once, but with a horse.) When you see how the narrative glides back and forth between the consciousnesses of the characters, shifting so smoothly you can barely see the seams, you'll see the subtleties of laying down narrative in the third person. Like any other kind of mastery, it looks easy on the page, but it's very hard to do. Hopefully a close study of it in a wide variety of writings will help show how such third person techniques might also benefit journalism, personal essays, memoir, or any other form of first person narrative.