In my early 20s, I had memorized every batting champion and pennant winner in baseball history, so I decided to tackle home run leaders next. I went to the shelf to retrieve the book that contained this information and it was nowhere to be found. I only thought I had put it there. The brain that had soaked up a thousand pieces of baseball information in the previous week failed me when I tried to recall where I had put the book earlier that day.

Probably all of us have had these false memories, but when the same delusion happens on a mass scale, it is dubbed the Mandela Effect. This refers specifically to the aftermath of Nelson Mandela’s death in 2013, when many persons were certain they had seen his funeral procession years earlier.

Another well-known example of the Effect is many persons thinking they recall a film that never existed, Shazaam, starring Sinbad. Also, the Berenstain Bears are frequently mis-remembered as “Berenstein.”

It’s unclear why these phenomenon happen. With the anthropomorphic grizzlies, it has been speculated that since “stein” is a much more common ending for last names than is “stain,” those who grew up with the Bears were exposed to many more examples of the former. This may have helped created a false memory, which would be easy enough since the stain/stein distinction was less important than the Bears’ personalities, appearance, and adventures.

As to the fictitious flick, persons likely confused it with Kazaam, Shaquille O’Neal’s tragicomic attempt at thespian arts. Shaquille and Sinbad sound somewhat similar, and the latter has Middle Eastern fantasy overtones, so the blanks were filled in with false memories.

As to the example that gives the Effect its name, when Mandela was released from prison in 1990, there was a march that may have resembled a beloved figure’s funeral procession in terms of length, attendance, tributes, and displayed emotions. His release and its immediate aftermath may be what persons are mistakenly remembering as a funeral.

Offering a more paranormal rationale is ghost hunter and psychic Fiona Broome, who wrote that this might be evidence of an alternate universe. As she describes it, we may move in and out of these universes, sometimes taking memories with us. But if this were true, we would also be sliding out to a reality where Mandela still lives and another where he overthrew the South African government in the 1960s, and no one is claiming to have recalled these circumstances.

Broome is not offering a testable hypothesis so there’s nothing substantive we do with her idea. Instead, let’s consider more reasonable alternatives.

Brains confabulate invented recollections to fill in memory gaps. We might, for example, misattribute later memories to earlier events, or think our childhood trip to the creek was with our best friend when it was really with his brother. These fabricated recollections are sometimes provided by someone else. While a few persons may have mistakenly remembered Hannibal Lecter telling the FBI trainee,  “Hello, Clarice,” many more people think they recall this line because they heard someone else saying it. Indeed, being exposed to a false memory can cause it to become implanted.

And if the false memory centers on something important to the listener, confirmation bias makes it even more likely to take hold. One of the Birther claims was that Obama’s step-grandmother was captured on tape talking about his Kenyan birth. No such tape exists, but Birthers continued to parrot it because the idea was attractive to them. Conversely, the 1990 New York Times article describing Obama as Hawaiian-born is not something they would be likely to remember.

So then, common cognitive errors are all that is needed to explain the Mandela Effect. At least that’s the case in our parallel dimension.