By Dennis Lowery
An understanding of the chronological sequence of events is important in storytelling, but not as important as the narrative sequence, which is the structure that: 1) brings readers in and hooks their interest; 2) keeps them reading; and 3) leads them and the story to a fulfilling conclusion. That’s how beginning, middle and end function in a narrative.
See the above link for an article from Writer's Digest on creating a narrative arc. Even with non-fiction or a memoir, it is a good idea to follow this arc when writing, to engage the reader and make for a more compelling story.