Rosemary finds herself unwilling or unable to deal with the burden of the memories she receives during the period of time when she is in training to become the next Receiver of Memories. Even though the Giver is selective about the types of memories he gives her, he cannot avoid giving her any type of pain.
And I didn't give her physical pain. But I gave her loneliness. And I gave her loss. I transferred a memory of a child taken from its parents. That was the first one. She appeared stunned at its end.
Rosemary goes to the Council of Elders and asks to be released from her assignment. She injects herself, as the "release" process is described, much to the pain of her father, the Giver. Since memories cannot disappear, they return to the entire community's awareness when Rosemary dies, causing members of the community great pain in the short term since they have no experience in dealing with pain.