This is evil and it destroys people. Let's just get that out of the way. Nonetheless, suppose you need to make someone distrust their own memory and perception of reality. Suppose you want someone to believe in you more than they believe in themselves.
Regardless of your malicious motive, the tool you're looking for is an insidious form of deception known as "gaslighting."
Gaslighting is basically "crazy making." It's most often used by sociopaths, cult leaders, lawyers, and bad boyfriends. The goal is to convince a person that they're insane and that none of their memories or beliefs are reliable. By destroying their trust in themselves, you make them totally dependent on you and essentially design their understanding of what's real.
I told you this was evil.
The psychological term originated with the play Angel Street and its subsequent Gaslight films, in which a husband attempts to convince his wife she is crazy by manipulating small elements of her environment.
And this was all just so he could get the jewels he failed to steal the first time. I won't spoil it for you, but you should really watch one of the film versions.
Calling people crazy will only leave you lonely, that is, unless those people are literally addicted to you.
When we excite someone we alter the chemical makeup of their brain by triggering the release of endorphins and dopamine. Using the same chemicals that provide heroin users with their high, a gaslighter hooks their victim before the manipulation phase. This is one reason why gaslighting is commonly used in romantic relationships.
Personally, when I think of a charming manipulator, I think of Hannibal Lecter. He's a terrible person, but from the minute he starts talking you're rooting for him. His charm, his intellect, his poise, everything about his personality is addictive.
We all misunderstand things, but that doesn't mean we misunderstand everything. A gaslighter, however, is sure to remember every mistake and misinterpretation their victim makes in order to later delegitimize their victim's ability to make a decision.
"Remember the last time you tried to do this..."
Eventually, the victim begins to see how often they are wrong and will turn to the gaslighter for solutions to their problems.
The gaslighter is the master logician and everyone else is wrong. When a victim makes an argument, the gaslighter will either dismiss it as illogical, unreasonable, blown out of proportion, or flat-out unreal.
The gaslighter later reveals the "correct" answer and presents it as "simple reasoning." Over time, this slowly dismantles the victim's trust in their own ability to reason.
Try telling someone that they didn't do something that they actually did. "I don't remember you doing that." If you're insistent enough and the event is small enough, like flushing the toilet or turning off the lights, you will see how easy it is to manipulate someone's memory. After repeated exposure, they'll begin to question the reliability of their own memory.
Remember how weird you felt at the end of Shutter Island? Well, before Leo's character lost his mind, Martin Scorsese sprinkled subtle events into scenes that left us unsure of our own recollection of events. He gaslighted us.
You could also go the other way with this technique, by telling someone that they did do something that they actually didn't.
Gaslighting drains its victims, leaving them depressed and insecure. They will begin to voice their concerns, at which time the gaslighter dismisses them as overly emotional and, of course, illogical.
Gaslighters convince their victims not to trust their feelings and instincts, and instead rely on the gaslighter as a source of reason.
There you have it. While this isn't a comprehensive guide (you won't believe how many techniques there are), it's enough to get you started. And while most of these tips use verbal communication against them, there are trickier ways to gaslight (think Amelie and the grocer).
While you probably won't be able to gaslight correctly on your first try, practice makes perfect. Mindfucking ain't easy, but it's definitely not impossible (nor entirely recommended).