The effect is real. The question is, why is it happening?
Whether it is "just happening" or "someone is up to something" is left to be decided.
In any case, it definitely "plays tricks" on the memory...
I have determined that the things I remember differently - really were not different.
I believe that we are "impacted" by things like - imagery that we see -- which is why the "lion and lamb" thing is prevalent. Seeing enough pictures of a lion and a lamb laying next to each other all our lives can have its impact on our memory - which, somehow, "takes over" when we think about the scripture with the wolf and the lamb.
With regard to the Zapruder film, I think 'focus' may have something to do with how many people we remember being in the car.
It is all interesting, nonetheless...