But some find that power through the techniques of fiction. Indeed, like novelists, many memoirists write pages of dialogue, even if the actual conversations took place decades earlier. They often create composite characters, collapse time, and fill scenes from long ago with lush detail.
"You're taking the highlights of your life. It's a work of art, it's selective, it's subject to memory," says memoirist Lili Wright, author of "Learning to Float" (2000). "A memoir is art, it's literature. It's not journalism, it's not a documentary."
For many memoirists, balancing reality with the art of writing is difficult.
"Every second of the process, you're confronting questions about ethics and the boundaries of what's true and not true," says Nancy McCabe, author of 2003's "After the Flashlight Man."
Some authors consult their journals and diaries. Others, like Ms. Karr, check with people featured in their memoirs and ask them to sign releases stating the books are accurate. This is a good idea, Karr says, not least because "most of the people in my family are armed."
In the larger picture, Karr says such consultations help keep her honest. "For me, the greatest pressure is to tell the truth to the best of my ability, knowing that it will be corrupt, and I'll forget things, and I'm self-serving."
In addition to fact-checking, some memoirists warn readers about the pitfalls of memory.
In his groundbreaking memoir "This Boy's Life," author Tobias Wolff notes that he and his mother disagree over the attractiveness of a dog in the book. He allows some disputed details to stand "because this is a book of memory, and memory has its own story to tell."
It's important to be clear and upfront with readers, says Patricia O'Toole, author of the 2005 biography "When Trumpets Call: Theodore Roosevelt After the White House." "You have to let the reader know what your game is. If you're telling the reader it's the way it really happened, it ought to be the way it really happened."