The term originates with a 1938 play called “Gas Light.” In the play, a woman’s husband tries to convince her that she is mentally unstable. He makes small changes in her environment, such as dimming the gaslights in their house. He then convinces his wife she is simply imagining these changes. His ultimate goal is to have her committed to an asylum so he can steal her inheritance. It is an abusive tactic aimed to make a victim doubt their own thoughts and feelings.