Mandela Effect

The Mandela Effect, or MaE, was a phenomenon where a large number of people apparently misremembered a significant event. The effect was named after the large number of people who remembered that Nelson Mandela died while imprisoned in the 1980s. In reality, he was released in 1990 and died in 2013.

As he described in an article on Into the Unknown, Professor Maxwell Grey believed a possible explanation of the phenomenon was people recalling the events of an alternate timeline that had been rewritten. One reader suggested the Mandela Effect could be the reason they remembered the Battle of Canary Wharf but their friends could not; whenever the reader described the metal men or other metal invaders from that day, their friends always had a faint moment of recognition on their faces before "check[ing] themselves" and saying the claims were nonsense. (PROSE: The Mandela Effect, Or Monsters on the Streets of London)

As the Seventh Doctor and Twelfth Doctor noted, humanity had a great ability to forget major crises, as the human race did not want to remember such events because such tragedies would fundamentally change human nature, making people stop fighting wars and having children alike. Instead, most of humans only remembered the fear they felt in the situations, placing that emotion into "fairy stories" they made. (TV: Remembrance of the Daleks, In the Forest of the Night)

Amy Pond had memories of a timeline with her parents and the timeline without her parents. The Eleventh Doctor confided in her that time is being rewritten all around them and that "people think their memories are bad, but their memories are fine." (HOMEVID: Good Night) Rory Williams could sometimes remember his nearly two thousand years as a Roman Auton, although it was like a "door in [his] head" he could keep shut. (TV: Day of the Moon, HOMEVID: Good Night)

Some citizens remembered the timeline where Felix Mather was President of the United States despite Faction Paradox rewriting history so that Barack Obama held the role. (HOMEVID: Ex-President)