The narrator is also a character in a first person novel, making for a more intimate perspective for the reader. Whether the narrator is the protagonist or a more minor character, the reader gets a sense of being closer to the action, among the other characters. A first person narrator can tell a story from the present, or from the perspective of an older, wiser self looking back on the events. In either case, the first person perspective gives the reader a sense of personally knowing the character.
Telling a story in first person allows an author to creatively withhold information. Readers naturally believe what a narrator tells them, but a writer may not necessarily create a reliable narrator. A first person narrator can be mistaken, lie or be insane, and a writer can choose to reveal the truth at a later point in a story. A writer can also hint at a narrator's unreliability, leaving the reader to draw conclusions about the level of truth in a narrator's version of events. Experimenting with reliability can lend suspense to a story and make for particularly interesting characterization. Creating a first person narrator who is less than sane, or who doesn't know or understand all that happens in a story can also make a story far more complex.
Since we use first person when speaking in real life, some authors believe writing in first person is easier than third. First person can be more straightforward, with a narrator who says what he feels and sees, rather than a narrator who describes what someone else feels. Writing in first person also requires a writer only to inhabit a single character's thought process, rather than switching between several characters' perspectives. Some writers argue that using a first person perspective simplifies the writing process.
Some writers argue against the effectiveness of a first person narrator. A third person narrator does not need to shift between viewpoints, but can tell the story from the perspective of a single character, making it nearly as intimate and simple as first person narrating. On the other hand, using a third person narrator who shifts between different characters' viewpoints allows for a more complex, multi-dimensional story. Ultimately, there are pros and cons to both first and third person story telling. Most authors agree that the most important factor in choosing a narrative viewpoint is the particular story. Successful authors know which stories require which viewpoints and why.