One difficulty in writing first-person prose is the inability to describe the MC’s personality and appearance. Because people rarely ever describe themselves (especially not as a narrator would), this can make visualization and emotional identification tricky; usually too heavy or too light. Because of this difficulty – in addition to other things, like a heightened sensitivity to failures of tone, and a tendency to feel claustrophobic – people tend to find first-person narratives harder to get into, and easier to fall out of. Most readers (and publishers) prefer third-person.
On the other hand, one advantage of the first-person POV is the ability to literally sit inside the character’s head. This can give your story a degree of conceptual continuity and reliability that an outside voice may not have, but that continuity will be subjective to the MC.
The second point should offset the first. The advantage must outweigh the difficulty.
When reading a first-person narrative, the MC’s subjective world becomes the reader’s default view, and you should be able to explain *why* you’re doing it that way. It’s not like first-person is the only way to interiorize the inner dialogue of characters; a semi-permiable omniscient narrator is all you need for that. In third-person works, it’s even possible to shift the POV from one character to another (usually by chapter but occasionally by paragraph); writers do this all the time. So you see, the shift to the subjective POV is not simply a stylistic checkbox.
Taken seriously, this will change everything about your story. In choosing first-person over third-person you are changing not just the “camera position” (as you might when choosing one POV character over another), but rather the entire teleological purpose of your tale. Rather than telling a story of characters doing things, you are enacting a character going through things.
This is a big difference.
A first-person work replaces the objective world with the internal world of the MC, going far beyond a mere change of camera position. A fitting metaphor might be to say that it provides a pair of glasses through which the world will be experienced, though this metaphor falls short because the world isn’t limited to vision, or even to material objects; it also includes feelings, emotions, connections, abstractions, motivations, relationships, etc. We have to imagine the glasses as not a camera position in the exterior world, but rather everything about the MC’s interior world, including the character’s own understanding of the exterior world. When the MC changes, the glasses change.
This takes us back to the poor reader, and the importance of offsetting their difficulty with your advantage. After all, one can’t put glasses on without being aware that they’re doing so, and therefore the fact that you’re even making them wear the glasses has to be justified. The justification will be found in the purpose of your story, and the purpose of your story will be interior. Instead of a stylized narration of ostensibly objective events, you are presenting the reader with a subjective monologue, a modulated chain of interior states, and you couldn’t do it any other way.
It is not an understatement to say that no matter what happens “out there” in the fictional world, the first-person story is actually about the glasses.
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TL/DR: Most readers prefer third-person POV. If the purpose of the story isn’t interior to the MC’s understanding of their world, the use of first-person should be questioned.