Who does the letter belong to? Does it carry the same meaning for both the writer and the recipient? And what if it never reaches its final destination?
For American author, Amy Bloom, the unsent letter is just as revealing as the one that arrives on your doorstep. "You think of the letter as existing between the writer and the reader, but of course it exists as soon as it is written. It reveals a lot about the writer. But it is also up to whoever reads it to interpret it in their own way," she says. Just like a book, then.
Bloom insists that, when it comes to her third novel, Lucky Us, which is full of sent and unsent post, it is up to her audience to draw their own conclusions: "My job is to form the people, the story, the sentences," she says. "Every reader will bring their own life and their own history to the story and shape it accordingly. I guess you can say it's like I am sending them a letter."
Born and raised in New York, Bloom, 61, has always been interested in the stories of passersby - an intrigue that grew through her training as a psychotherapist. People are rarely as they seem.
No surprises, then, that throughout Lucky Us - a tale of two half-sisters striving to achieve the American Dream against the backdrop of the wartorn 1940s - people and events are constantly shape-shifting.
Characters change identities; starting and ending their lives without forewarning; and hide behind various personas. She says the novel's ambiguity is symptomatic of the era: "I find the 1940s very compelling. It is a very excitable period in the US when, whether out of necessity or not, everybody was reinventing themselves. Your role changes all the time; no one is born 'Aunt Suzy'."
In Lucky Us, Hollywood actors deliver their lines, and then maintain their screen identities for the audience and the media once the camera is switched off. Characters with Jewish backgrounds and Yiddish mother-tongues wipe their histories clean with new names and refined speech. And young women - almost children themselves - are forced into roles of mother and teacher.
"I love the secret preparation for the performance, when people are redoing their make-up or sitting in the dressing room," Bloom says. "And I think that, for lots of people, not just in my book, there is more of that than you would expect.
"As children, we think our mother has always been a mother but it is just one of the roles you may have the opportunity to play. They don't define you as a human being."
"You see a photograph of a happy moment," Bloom says. "If someone is inclined to see that as a happy ending, then I think that is lovely. But life continues after the photograph is taken."
Bloom says that the variety of her many roles - fiction writer, mother, psychotherapist, English professor and children's author - has enabled her to observe people, and channel her characters' individual voices accordingly.
"If the characters are not alive to me, it doesn't matter how good the sentences are," she says. "It just becomes all cake and no frosting." In other words, it is all in the letter's delivery.