I think the whole Mandela Effect comes from how the human brain fills gaps with details or adds memories to things that never really had those memories.

I might get downvotes as hell for this but that is exactly what it is. Nobody denies the Mandella effec on its ownt, but the explanation is far simpler (and really interesting in my opinion) than it seems. Think about it this way: as a species, our brain is capable of incredible things bu in the same time it can't remember a simple logo or movie quote.

By the way, nobody says your memory is bad, because it's not. Our brain is just weird like that. We only remember general details regarding these matters, enough to recognise it when we see it. But without a visual cue, our brain has no freaking idea how famous quotes, basic geography or famous logos are supposed to be.

There was even that (already) famous selective attention test, which proves exactly how weird our mind is. I won't tell you the punch line because it will ruin the test.