“Because memory is reconstructive, it is subject to confabulation—confusing an event that happened to someone else with one that happened to you or coming to believe that you remember something that never happened. In reconstructing a memory, people draw on many sources. When you remember your fifth birthday party, you may have a direct recollection of your younger brother putting his finger in the cake and spoiling it for you, but you will also incorporate information that you got later from family stories, photographs, home videos, and birthday parties you’ve seen on television. You weave all these elements together into one integrated account. If someone hypnotizes you and regresses you to your fifth birthday party, you’ll tell a lively story about it that will feel terribly real to you, but it will include many of those party details that never actually happened. After a while, you won’t be able to distinguish your actual memory from subsequent information that crept in from elsewhere. That phenomenon is called “source confusion,” otherwise known as the “where did I hear that?” problem.”