"One of the saddest sentences I know is 'I wish I had asked my mother about that.' Or my father. Or my grandmother. Or my grandfather. As every parent knows, our children are not as fascinated by our fascinating lives as we are. Only when they have children of their own—and feel the first twinges of their own advancing age—do they suddenly want to know more about their family heritage and all its accretions of anecdote and lore. 'What exactly were those stories my dad used to tell about coming to America?' 'Where exactly was that farm in the Midwest where my mother grew up?'"
"How to Write a Memoir" by William Zinsser
According to Zinsser, what is the main reason why a person writes a memoir?