When it comes to writing, the author and the speaker are two different things. The author is the person who wrote the story. The speaker is the person who tells the story. In One Flew Over the Cuckoo's Nest, the author is Ken Kesey and the speaker is "Chief". Every time in the book you see "I saw. . ." or "I did. . .", we understand that Chief saw or did whatever.
This is not a difficult concept to understand, but there are a few tricks to it. For example, the author and the speaker can be the same person. Creative non-fiction is almost entirely based on the author speaking to us. But when we read non-fiction, it is usually safe to assume that the author and speaker are one.
The real problems usually come from poetry. Poems rarely give us any bearings. Good poetry is short, sweet, and to the point. Therefore, when the poem is first person, we have no idea who the speaker is. It could just as easily be a character as it could be the author unless enough clues are given to distinguish them.
You may be wondering what the point of any of this is. Truth be told, it's mostly a pet peeve when people assume that the speaker is the author. However, I also don't like the tendencies it causes. When we assume that the speaker is the author, we assume that the speaker is always the author, which makes us think that the speaker should be the author, or that the speaker must be the author. When we reach these points, our writing suffers. We lose vast amounts of possibilities in writing when we only focus on ourselves as subjects.
That is why I feel it necessary to remind people that the speaker and the author are different people. I think that people should get out of their own head more often and write about things that aren't themselves. They should explore all of the possibilities they can, not just the ones that are the easiest to come up with. I'm not saying you shouldn't do personal first-person writing. I'm doing it every time I write in this blog. However, outside of this blog, my work is across the spectrum and I am proud of that.