You're presupposing linearity, when in fact it's entirely possible that our reality is just a particular branch of infinite branches. In other words, it *didn't* actually have to happen the way it has. Imagine our current reality as only a more likely point in space-time, while flawed realities gradually prune themselves off. We may be a flawed or incomplete reality as well--or a figment of someone else's imagine, I suppose.
The rabbit hole always goes a bit deeper than you think
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