In the 1930s there was a play ‘gaslight’ about a husband manipulating his wife into believing she is insane. ie. dims the gaslights in her home, insisting nothing has changed.
People who gaslight use things like denial, contradiction, misinformation, misdirection and even true information and facts to destabilize, disorient and delegitimize a person’s sense of reality.
When someone is gaslit, they end up in a state of extreme cognitive dissonance. Doubting one’s own sense of sanity leads to a severe decrease in self-esteem. They learn to distrust their own mind and thus defer to the perceptions and control of the person gaslighting them.