Boltzmann Brain
I find this question really fun: "Am I a Boltzmann brain, or a real human?". If there exists both a human and a Boltzmann brain with your current mental state, then it doesn't make sense to try to answer this question with a single answer. Your line of reasoning will be identically executed in both, so your line of reasoning can't result in a single answer and be correct.<p>Instead, one way to address the confusion about whether you're a Boltzmann brain or not, is to realize that in the case you're a Boltzmann brain, none of your thoughts or decisions matter at all. Even if you admit there's some probability that you're a Boltzmann brain, there's no use factoring it into your decision processes besides as a curiosity. Your decisions only matter in the case that you're an actual human, so that's the only possibility worth considering while coming up with decisions. (Similarly, if a coin was going to be flipped in a moment, and a bunch of things depended on which way the coin landed, including that you were going to be immediately executed with no possibility of escape if the coin landed on heads, then all your plans for the future should be exactly the same as if you expected the coin to land on tails with 100% certainty. It's the only path that any of your decisions matter.)