A friend of yours lost her father to cancer when she was a very young child. “I really wish I remembered him better,” she says. “I know all the memories are locked in my head. I am thinking of trying hypnotism to unlock some of those memories.” You explain that we do not, in fact, have stored memories of everything that ever happened to us locked in our heads. What examples could you give of ways in which memories can be lost over time?

Another friend of yours has a very vivid memory of sitting with his parents in the living room on September 11, 2001, watching live television as the Twin Towers fell in New York City during the terrorist attacks. “I remember my mother was crying,” he says, “and that scared me more than the pictures on the TV.” Later, he goes home for a visit and discusses the events of 9/11 with his mother—and is stunned when she assures him that he was actually in school on the morning of the attacks and was only sent home at lunchtime, after the towers had fallen. “I don’t understand,” he tells you afterward. “I think she must be confused, because I have a perfect memory of that morning.” Assuming your friend’s mother is recalling events correctly, how would you explain to your friend the ways in which his snapshot memory could be wrong? What memory sin might be at fault?

You ask one of your psychology classmates if she wants to form a study group to prepare for an upcoming exam. “No offence,” she says, “but I can study the material best by just reading the chapter eight or nine times, and I can do that without a study group.” What is wrong with your classmate’s study plan? In what ways might the members of a study group help one another learn more effectively?

You and a friend go to a party on campus where you meet a lot of new people. After the party, your friend says, “I liked a lot of the people we met, but I’ll never remember all their names. Some people just have a good memory, and some don’t, and there’s nothing I can do about it.” What advice could you give your friend to help him remember the names of people he meets at the next party?

A friend of yours who is taking a criminal justice class reads about a case in which the conviction of an accused murderer was later overturned, based on DNA evidence. “It’s a travesty of justice,” she says. “An eyewitness clearly identified the man by picking him out of a lineup and then identified him again in court during the trial. No results from a chemistry lab should count more than eyewitness testimony.” What is your friend failing to appreciate about eyewitness testimony? What sin of memory could lead an eyewitness to honestly believe she is identifying the correct man when she is actually making a false identification?