If only I could have a second chance!
Rav Sholom Shwadron used to give a parable. He would paint a picture of neshamos, departed souls from the Next World, allowed to come back down for one hour, just one hour.
He described the scene, how they would cherish each minute, fully aware of what each mitzvah in This World means in the Next: They would run to learn, to daven, to give tzedakah, to say a kind word and apologize to those they may have hurt.
"Just one hour", he would thunder, and then look around the room. "And we" - his voice would drop - "We are here, right now. Let us live like we have just one hour!"