on Jane Friedman site:

Every story is about transformation. The main character’s journey changes them in some way; that arc, in turn, affects the character’s perception of the world around them.

In memoir, you are that main character. While fiction writers can invent entire worlds and determine how much of that world is revealed to the narrator, memoir is expected to be first-person (most of the time) and to reflect the author’s truth (all the time).

While fiction writers can play with unreliable narrators (narrators who are either lying or don’t have the self-awareness to realize that their perceptions are inaccurate), memoir readers expect that the narrator is being honest in each moment; this provides a sense of internal coherence and enables the reader to trust the narrator. If you break the reader’s trust, you’ve lost not only that reader, but also their recommendation of your memoir to others.