You have reached the most crucial part of the paradox.
Imagine a man named John who, as a young adult, traveled back in time, killed his own grandfather, and in doing so, was born. But since he was never born, he could never have killed his grandfather, which means he was born.
But here's the thing: if John was born, then he must have had a grandfather, right? So, if his grandfather was alive when John killed him, that would mean John wasn't born. But if John wasn't born, then he couldn't have killed his grandfather, which means... ...read on, brave time traveler!
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