Mandela Effect

The Mandela Effect is a recent phenomenon that is believed to be caused by confabulations, or false memories, involving certain events happening at different times that "were believed to be remembered", and different spellings of products "than perceived". The term was coined by Fiona Broome, a paranormal consultant, in 2010 [1]. Some believe most older millennials and generations before were born in an "alternate universe" but were shifted into another one within the past several years (thus explaining the minor differences).

Berenstain Bears
Perhaps the most prominent example of the Mandela Effect is the Berenstain Bears, a popular American children's book series and cartoon. Thousands, perhaps even millions, of millennials who once watched the TV series, as well as the younger baby boomers who were read the books as children, remember the spelling as "Berenstein" rather than the correct "Berenstain". YouTuber SEFD Science published a video in September 2015 trying to disprove the "alternate universe" theory (that is, in the alternate universe it was spelled "Berenstein") (Video Here). SEFD Science in the video says that "recalling a memory" in reality is actually not recalling it at all, but rather "reconstructing it from from nothing or from scratch" [2]. YouTube channel New Rockstars lists examples in TV Guides that do have the spelling as "Berenstein" as well as a book where Panda neighbors move in, which according to the cover shows "Papa Bear" pissed off (possibly proving Papa Bear is a WASP) [4].

Occam's Razor
Occam's Razor is a philosophical aspect basically stating that the simpler assumption of two (or more) assumptions is more likely to be true. The more assumptions you make, the less likely it is to be true [2] [3]! SEFD Science uses this explanation to help explain his mis-remembrance of the series being spelled "Berenstein"[2].

Spelling/Suffix Popularity
For the Berenstain Bears conspiracy, another explanation made by SEFD Science is the popularity of the suffix "stein". Mike Berenstain, son of the late Stan and Jan Berenstain (creators of the book series), submitted an email with a link to a recalling in an autobiography by Stan Berenstain. This recalling was during Stan's 4th grade year during roll call when the teacher stated "there was no such thing as a 'Berenstain' spelling" [2].