If you traveled back a few decades and killed your grandfather when you were young, then your father would be gone, and you would be gone too. Since you no longer exist, you can't kill your grandfather. If your grandfather doesn't die, you can exist again and go back to kill your grandfather...
So this is a little story built on a paradox, asking: does your existence exist?
Yuan Jie said: "The poor monk has his own way of life and nowhere to return."
Jiang Zuo said: "I will die in the history of traitors and sycophants. How about that?"