I think the Mandela Effect is as much about people wanting to fit in as it is about poor recall. If you and I were discussing a movie we watched last night and I slightly misquoted a line from the movie, but you aren't certain enough to correct me; you will just accept my quote as correct. That's how human psychology works. We all have a tendency toward wanting to fit in and not mess with the accepted status quo in a particular circumstance. All of the examples I've ever heard of the Mandela Effect fit this idea.
I believe Shiloh is 100% correct in saying that God will work to protect His Word. And, Abby, I think you are missing the point in having different translations of the Bible. There are two basic styles of Bible translations. Word for word, and dynamic equivalence. The difference between them is that a word for word translation (like the NASB) will attempt to translate the Bible as literally as possible into its contemporary language. Remember that language changes over time. The definition of a word can change drastically over centuries, sometimes meaning something completely different over time. A dynamic equivalence Bible will attempt to skirt that problem by using a different word or phrase to express the same idea. The most extreme dynamic equivalence Bible is The Message. Neither style of translation is inherently right or wrong. Both are simply trying to preserve the truth of God's Word for each new generation. I get that a lot of people tend to dismiss The Message as being shallow or watered down, but it's actually a great tool for understanding some things within context that a literal translation may not get.
For example, Paul often uses euphemisms when talking about Jews and Judaizers. He calls them things like "the circumcision." If you don't know the context to grasp that when Paul says "the circumcision" he is talking about a group of people, you can make the mistake of assuming that Paul is literally talking about the act of circumcision. Now over the course of generations, Bible translators work to keep these wordings accurate and contemporary by revising or making all new translations. This is a good thing. Not everyone has the ability to take Greek or go to seminary to learn all the tiny intricacies of Biblical references and context. So it's the job of the translators to keep the wording up-to-date so that anyone reading it will still understand what the writer meant to say.