Hey Robin, why don't you solve the Grand father paradox?
I am glad you (didn't) asked.
Well imagine for a doubtful reason that I wanted to get rid of my grand father.
I travel back to the past. Yet if I kill him, that would mean I would not have existed in the first place.
So you didn't participate to the party in this universe for one reason.
You did travel to the past and met him on a parallel universe.
Welcome to the multiverse.
Why didn't a Robin from another universe come and make Hitler's Mom come? 😂