"You have more chance of reanimating this scalpel than you have of mending a broken nervous system!" - Frederick "Fronkensteen" on why "Dead is dead."
In the case of Brett Favre, I would say Doctor Frankenstien, excuse me, Fronkensteen has hit the nail on the head. To aid in this discussion, I have brought with me two bits of evidence. First let us examine the various careers of the greatest basketball player ever, Michael Jordan. MJ had already cemented his position in NBA history before he decided to retire and try to do the same with Major League Baseball. His impact was not quite as substantial on the base paths as it was on the hardwood. So he came back. But he had lost some of his magic, as was apparent by the way the Bulls lost to the Magic in the semi-finals. Then he bounced right back and won three championships. Go figure. Then he left again, only to resurface in a Washington Wizards uniform, where he was barely recognizable as the man who once soared through the air, delivering MVP and championship trophies to the fans in Chicago. Now all that's left are his shoes.
My other example comes from the NFL: John Elway. Admittedly, I have a certain personal connection to this case, but there are few that would say that Elway didn't go out on top. He won a Super Bowl, got that monkey off his back, and then showed up next season to prove it was no fluke. He won the MVP award in the championship game, and he walked off the field a winner. He held his tearful press conference, and he was done. Sure he shows up now and again in some regrettable TV commercials, but he's not out there trying to recapture a time that has passed. I've got a ton of respect for Brett Favre's competitive fire, but it's time to pack it in, and let some young guys take over. Does the world really want to see "Favre" on a Minnesota Vikings jersey? I hope the next time we see Brett, he'll be selling some of those Wrangler jeans he likes so much.