Wherein lies the heart of time travel paradoxes? It's not the Grandfather, the Bootstrap, or even the Predestination. Nay, it's the Novikov Self-Consistency Principle that's the real brain-twister. This Russian physicist's 1964 paper posited that any closed timelike curve would be self-consistent, meaning the effect of an action would only be observable if it's consistent with the timeline leading up to it.
Read more about Predestination and the Butterfly Effect! Counterarguments: Why the Novikov is actually just a bunch of nonsense Examples of Novikov Self-Consistency Principle in action (or not) The Physics behind Novikov's Self-Consistency Principle