Well, I guess if someone ever came up with a reasonable answer to that question, we'd all be walking stiffs. Then again, maybe some of us already are. The question is, how to tell if you're a walking stiff. I remember a show about some astronauts who were in a space shuttle when the world blew up. The took an opportunity to go back in time to try stopping the event. I think that was a show where they didn't really know who were the bad guys [aliens] and who weren't. I really liked it. It was on the SciFi Channel, or Showtime, but I think it got canceled in the first season. Bummer.
Writing prompt by http://writingfix.com/dailypromptgenerator.htm.