Glenn Close’s unforgettably vivid portrayal in the movie Fatal Attraction gave viewers a front-row look at the damaging mental illness known as borderline personality disorder (BPD). By itself, this ailment accounts for up to 10 percent of patients under psychiatric care and 20 percent of those who have to be hospitalized. The defining characteristic is pervasive instability in the patient’s life, especially in relationships. People who suffer from BPD also have difficulty controlling their impulses and regulating their emotions. Their behavior exerts a tremendous toll not only on themselves but also on their friends and colleagues, as well as on the health care system.