In summary: If you object that "a particle can't be in two places at once", the answer is that you are trying to use a classical concept of "particle" and that concept is not what we're talking about here.In summary, Zee says that a particle in QFT is a localized wavepacket, and that the double slit experiment is not able to account for them because you need to use two wave packets to model it.
Due to the rampant personal speculation of the OP this thread is closed. Thanks to all who made a sincere effort to resolve it through instruction rather than moderation.