Time paradox

lets take an example.

A man travels back in time and does something insignificant, thus "butterfly" effect goes haywire and he winds up never having been born. BUT if he was never born how could he have gone back in time and caused said time paradox to stop him being born?

Travelling backward in time and changing anything creates a Paradox.

If you go back in time and change something as you see fit, the result will be that, obviously, what you wanted to change never happened because you changed it, therefore you didn't go back in the first place, so it still happened.

That is the nature of a Time Paradox.