According to Dr. Keating, there are two determining factors in whether someone will intervene. "One of the first things you have to do before you intervene is take personal responsibility. It's risky. It's costly. It can cause embarrassment. … In Tammy's case, you might really endanger yourself physically," she says.

The second factor, Dr. Keating says, is empathy. "When you empathize with the victim of aggression, it creates a whole different reason for you to take responsibility and try to do something," she says. "Unfortunately, the psychology of human beings is often that if we perceive someone to be different from ourselves, we treat them differently and oftentimes unfairly."