 You could have turned left at an intersection or you could have turned right, and your whole world, your life is different based on that choice. Usually it doesn't matter that much, but a small decision like that can have all sorts of implications. And so that's where this idea comes in. And if it's true, which it seems to be, that we are experiencing these other worlds, then we would expect from time to time to see that the world is slightly different than we remember it.