My family brought me up the Eiffel Tower when I was very young but I have no memory of that particular instance. I don’t remember a great view of the city or waiting in line at the bottom. I don’t remember using an elevator or climbing up stairs. I know that I was on the Eiffel Tower and I consider it an achievement somehow. Truth be told, you are one YouTube video away to have a better idea than me about what being on top of Paris feels like.
I don’t remember entire chunks of recent travels either until I see a photograph. It’s barely a trigger, it’s merely proof. Then I mostly remember what that photograph looks like and after some time, that one single image becomes my new memory of the experience and a basis for nostalgia.
Now imagine opening an old private camera folder and one inconspicuous picture, not yours, had been transfered inside. If it’s nothing too crazy, if it makes sense and there’s context, certainly you would own the experience without thinking too much about it.
When you’re dreaming about past memories, this forgery happens by itself. Then you might dream again and again about that inaccurate dream. At this point it becomes very hard to know if there’s a speck of truth left to it. I said dreaming but conscious thinking is of course prone to the same problem.
With the rise of immersive VR technologies and machine learning (deepfakes, chatbots, etc), it might become easier to merge false memories with the real ones. It could be used for fun or as a tool to de-emphasize traumatic experiences or something.