Great article about what goes into writing a memoir. You aren't just methodically putting down experiences, but choosing the ones that not only tell a tale, but tell something about you as a person and how that experience shaped you and moved you towards who you are today.
I am just finishing up my own memoir and can confirm that it was an enormously difficult task. Only when forced to formulate experiences into words do you have to tangle not only with the "what" but with the "why" - and the long-term impacts.
For me, it was the devastating impact that a move to the suburbs had on my family when I was just 5. It ripped my mother out of her wonderful neighborhood network of moms - and replaced it with a big house and yard.