The reason why this concept is so huge is because it's just not alternate realities. Scott's incapable of explaining, "In the reality I Shifted from, this person was a Very Bad Guy, which is why I suspect them of being the Big Bad in this reality." And I can't grasp why he can't say it! Everyone KNOWS a major Shift happened, they just don't know what was going on in the original world. And everyone knows Scott's memories from the new reality haven't fully returned, and everyone's OK with that. They all know a huge Shift happened, yet no one's talking about it or trying to get Scott to undo his Shift and take them out of a world at war, which is all they've known.
I often feel like my brain's expanding when I read these books.