Well, there is a bit of truth to reincarnation -- every living thing is the same identical subject. In essence, it's the existence-consciousness (i.e. "ontological basis") who sort of reincarnates as distinct individual entity. You can say that, currently on Earth, there's eight billion human reincarnations of the same "I". And of course there are also animals, etc.

Furthermore, exactly as we, who are currently alive, are the result of past causes and effects (which naturally includes acts of other people), so future individual beings will be results (also) of our lives, actions, etc. That's where the concept of Karma comes from. We can predict what life circumstances we create with our actions because, while there is randomness, free will, and so on, consequences are largely deterministic. And again, that future individual will have the same notion of I-ness as you and I have, because they will inevitably be the same "I" we all are.