Stockholm Syndrome is a common plot device in movies and books. But the psychological phenomenon—which was made famous in 1974 by Patty Hearst (above), the heiress who was kidnapped but later participated in a bank robbery with her captors, the Symbionese Liberation Army—is much more rare in real life. This makes it hard for experts to study, and even prompts them to question whether Stockholm Syndrome is actually a syndrome.

Nils Bejerot, a Swedish criminologist and psychiatrist, reportedly coined the term Stockholm Syndrome in 1973, following a bank robbery in Sweden in which four people were held for six days by their captors. Once they were rescued, the victims all defended the robbers and refused to testify against them. Since then, other similar instances have occurred, but not nearly enough for clinicians to create a list of criteria and treatment strategies for its inclusion in the American Psychiatric Association's DSM handbook.

That said, psychologists do know some things about Stockholm Syndrome, gleaned from interviews with people who have been held in a hostage situation. By watching the video below, you can learn what we do know about the rare condition, and why individuals might develop it, according to SciShow Psych.