Lunatics are similar to designated hitters. Often an entire family is crazy, but since an entire family can't go into the hospital, one person is designated as crazy and goes inside. Then, depending on how the rest of the family is feeling that person is kept inside or snatched out, to prove something about the family's mental health.
Susanna Kaysen, Girl, Interrupted (Faber and Faber Screenplays) Screenplay based on the book
crazy, family, mental-health