It's a sad moment, one that happens inevitably to all great athletes.
In football it can come in an instant—one moment Emmitt Smith is gliding through a crack in the line, plowing a linebacker and heading for daylight. The next, he's on the Arizona Cardinals and picking himself up behind the line of scrimmage again and again.
Basketball's Michael Jordan went the same way. In the blink of an eye you go from soaring above the rim with the world champion Chicago Bulls to standing around yelling at your teammates, somehow a Washington Wizard, to sporting a Hitler mustache in an underwear commercial.
In combat sports, a fighter can measure his mortality by the number of young guns looking to make their names on the back of his accomplishments. Those looking to use him as a measuring stick, to show fans, sponsors and matchmakers that they're no longer prospects. Boys looking to become men.
BJ Penn, once the champion of the world, once feared by fighters in two weight classes, is now just an opponent.
Rory MacDonald, who called out Penn Monday and received an affirmative yesterday, isn't afraid of BJ Penn. He doesn't see a legend looking to fight his way back to the top. He smells meat. Fighters up and down the card do. BJ Penn isn't a challenge anymore in their minds—he's an opportunity.
It's an important part of the architecture of athletics. Penn and other legends (like contemporary Matt Hughes, who faced many impromptu challenges once it was clear he was no longer in his fighting prime) are supposed to build the next line of stars.
This has been the way of the world for decades. In 1951, Joe Louis took one on the chin to build the legend of Rocky Marciano. Last month, "Sugar" Shane Mosley made a man of Saul Alvarez. It's how stars are created in this industry. And that's fine.
But Penn has already done his part. He lost twice to lightweight star Frankie Edgar, transferring his own credibility to a new generation of champions. Osmosis by fisticuffs. Had he stuck to his retirement, he could have left the sport with his head held high.
We wouldn't have any sad memories of BJ Penn in over his head. Of BJ Penn—who once knocked out Caol Uno in seconds and sprinted out of the cage, who relished tasting his opponent's blood, who upset the great Matt Hughes—looking overwhelmed, sad, old, waiting for that burst of energy that will never come.
Like so many before him, Penn doesn't know when to quit. And so the sadness will come. Inevitably, BJ's struggles will remind us he is mortal, and in doing so, he'll remind us we too are one day closer to death. We'll struggle to remember Penn as he was in his youth, but the memories of his late career failures will linger, impossible to forget.
BJ Penn had done things the right way. He was a champion and no man's stepping stone. Opponents once met him in the middle with a glint of fear in their eyes. Now he's nothing but prey, waiting to take his lumps from a new cast of predators. It's sad to see him back like this.