Return to Sender
Carol and Therese's relationship begins with a letter, and Carol's marriage ends with a letter. In between are a lot of letters that Therese writes but never sends.
Remember, this is the age before e-mail, so letters are a primary form of communication. For her part, Therese often uses them to work out her thoughts and feelings to Carol. She writes, "I feel I stand in a desert with my hands outstretched, and you are raining down upon me" (13.4). Maybe it's a good thing she never mailed that one—it's so cheesy.
However, for all the letters she writes but never sends, Therese takes a risk when she sends Carol the Christmas card that starts their relationship. She signs her employee number instead of her name to protect herself a little bit, but it's still a bold move. Perhaps this is what Carol means when she says to Therese, "I remember your courage that I hadn't suspected, and it gives me courage" (20.50). It's a lot easier to not send a letter than to send it, especially to a complete stranger.
Unfortunately, one of the letters Therese doesn't send becomes Harge's "strongest weapon" (20.49) in his divorce from Carol. In an ironic, though, if Therese had given the letter to Carol—and told her how she felt earlier on—they might not wind up together because Carol might have stayed married. Without the letter, Harge's case against his wife is much weaker. Go figure.