Obvious spoilers below.
The premise of this book is that every alternative, be it a choice or a random event, results in a “fork in the road” that creates a new universe for each possibility. So, in one universe, you chose option A; in the next universe, you chose option B. As a result, there are an infinite number of universes, and an infinite number of universes are being created every moment.
That is why, when “Jason 1”, our protagonist, was visiting various versions of Chicago via “the box”, each visit resulted in new universes and new versions of Jason 1. In keeping with the physics of the book, there should be an infinite number of these new versions of Jason 1, and in fact we do learn of hundreds.
Yet, despite this, the book portrays only a single universe in which “Jason 2” is living with Daniela and Charlie. And hundreds of copies of “Jason 1” descend on this universe.
But this makes no sense. In much the same way that every decision Jason 1 made while exploring “the box” resulted in a new universe and new copy of Jason 1, every decision Jason 2 makes in Jason 1’s original universe results in an infinite number of copies of that universe as well. So there isn’t just one universe in which Jason 2 has stolen the life of Jason 1; there are an infinite number of those universes and thus an infinite number of “original” Danielas and Charlies.
And because there are an infinite number of universes where Jason 2 has stolen the life of Jason 1 and is living with the Daniela and Charlie, the odds that another Jason 1, let alone hundreds of them, would descend on the exact same copy of that universe — one of an infinite number — is zero.
by trytoholdon