People use the term loosely now. True gaslighting occurs when one person refuses to validate your perceptions, feelings, or memories.
They do it because gaslighting works. Gaslighting is a way to manipulate and control you.
They're dictating the situation's reality (whether it's happening now or in the past) to gain control.
You recall a past event or discussion. You have a clear memory of what happened, but they say, "That never happened" or "You should see a neurologist." I think your memory's off.
Even though you chose the destination, hotel, plane, and activities, your partner says, "I put it all together."
This was my idea. I want to go there." If things go wrong, they blame you: "You forced us to go there, I never wanted to go there, and your bad attitude ruined the trip."