It is called the Time Traveler's Paradox. In which a scientist creates a Time Machine and kills their younger self. So now a man who should not- can not- exist, somehow does. That is the Paradox, and Paradoxes are impossible.
1914
1962
2013
2021
2016
2023
2014
2019
2015
2022
1932
1971
1984
1967
2018
