The Mandela effect is a basic flaw of human memory, called General forgetting. You WANT to believe that your childhood thoughts must have been true, or that memories are like recorded files ... and they aren't. Berenstain Bears is the best one for an example there. There are actual books with typos going around, but the family had that name. I even recall thinking "Wow I wish that was stein" as a kid. False memory is normal; people believing in universe hopping just because they agree with them ... that's crazy.
General Forgetting is probably right for most cases.. but when a whole group of people swore they remembered the same thing before but it is different now... kinda weird.
Mirror Mirror on the Wall vs Magic Mirror on the Wall, or the Forrest Gump's "Life is a life a box of chocolate" threw me off.
Sex And the City - not so much. Barbara Streisand threw me way off