Discovering a major problem at work, Doug called Joan and discussed the problem with her at length. A few minutes later, his coworker Latesha called him, and Doug told Latesha about the problem. Later, Doug told a friend that Joan had said that fixing the problem would cost $10,000. But later when he looked at his handwritten notes of the two phone conversations, Doug discovered that Latesha, not Joan, had actually made the remark. The contradiction between what really happened and Doug's memory can best be explained by: