A family member of mine is a professor and he left high school education after a woman began following him around town in her car and stalking him in places like the mall and movie theater - this was in the late 1980's in SoCal. At first he thought the woman was trying to express interest in him, but he was shy. One night in front of a bar with his teacher friends he saw she was driving down the street. So he stepped off the curb to wave at her to invite her to drink with them and instead she tried to run him down with her car. She missed him, hit the curb, and then proceeded to drive down the street into the back of an empty parked car. She was arrested and charged.

Long story short: She became convinced that he was dating her daughter because she found a love letter her daughter had written to him but not actually sent to him. Instead of doing the rational thing like talking to the principal she spent months seething with anger and hatred to the point it formed her intent to murder a man she had never even spoken to.