Brett Favre went on national television to try and explain something he couldn’t quite explain. He’s got plenty of company, because when it comes to retirement there aren’t many athletes who can figure out when it’s really over.

Sandy Koufax knew because his arm told him so. Jim Brown and Barry Sanders got out while still in their prime, too, for reasons that went beyond football.

But for every Koufax, Brown or Sanders there’s a dozen Favres trying to hold on even as their skills fade and the inevitable aging process takes over. The great Johnny Unitas wasn’t immune when he tried to stretch his career in San Diego, and Michael Jordan couldn’t even make the playoffs when he ended his second retirement to play two final seasons with the Washington Wizards.

Muhammad Ali couldn’t escape punches that sadly may have cost him more than his reputation, and Joe Namath couldn’t escape defenders as he tried to play on creaky knees for the Los Angeles Rams.

And who can forget a 42-year-old Willie Mays stumbling and bumbling around in the outfield in the 1973 World Series for the New York Mets.

They play because they still think they can play. They play because the money is good.

A lot of them play because they just don’t know how to quit.

“The easiest thing is to become an athlete,” former heavyweight champion George Foreman said. “But how do you get out? The sad thing about it is so few have been successful in doing that.”

Foreman ended up being one of those, though it helped that he had a second career as a grill pitchman that made him more than he ever made in the ring. But even he retired twice and was in the gym training for yet another comeback at age 55 before his wife squashed the idea.

Favre, of course, famously threatened retirement for a few years before tearfully announcing in March that he was done after 16 seasons with the Green Bay Packers. Like many before him he almost immediately had second thoughts and said Monday in a televised interview that the Packers helped push him out the door.

“I am guilty of retiring early and there is a reason for that,” Favre said.

The Packers deny that, saying they urged Favre to play and moved on only after the quarterback remained noncommittal and they had to make a decision. The team found itself in the uncomfortable position of having to finally say no to a sure Hall of Fame player, something the Mets nearly faced in 1973 before intermediaries finally persuaded Mays to retire.

“I can’t even mention the word ‘retire’ to him,” Mets chairman Donald Grant said at the time.

Money is almost always a factor in players wanting to stay, and Favre had about $25 million remaining on his contract with the Packers. But it goes beyond that, Foreman said, beginning with the admission that every athlete has to eventually make that his or her body is not what it was in younger years.

“When you retire you’re basically saying to yourself that my body is no good anymore,” he said. “That’s something no one will admit to. To look in the mirror and say you can’t do it anymore is so hard.”

There’s more, of course, including the fear of losing the sense of identity that has been with most athletes since they were playing Little League baseball or youth football. Suddenly you’re without the game that has defined you, and without the camaraderie of teammates that have always been around.

And then there are the perks of being a star player, from the adoring fans to, yes, even the media.

“You don’t understand how it is when you’ve got a guy with pen and paper turning the pages of his notebook over and over again, filling them with what you have to say. And behind him there’s another one in line and then another one,” Foreman said. “And then you wake up the next morning and not even your kids want to know what you have to say.”

Indeed, Favre’s attempted unretirement filled a lot of notebooks and ate up a lot of air time. He’s suddenly hot again, though not for anything he did on the field, and on center stage for yet another drama about whether he’ll have to be dragged kicking and screaming into retirement.

There are signs, though, that this drama may be getting a bit old around the edges, too. An unscientific newspaper poll found less than half the fans in Green Bay want Favre back as their starting quarterback, and a rally in his support in Milwaukee on Monday drew only about 30 people.

Foreman, who became the oldest heavyweight champion when he knocked out Michael Moore at age 45 in 1994, had the same kind of trouble retiring for the second time after losing to Shannon Briggs in 1997. He hatched plans to fight Larry Holmes in a battle of old heavyweights in a fight that never happened, and was in the ring training for another comeback four years ago before his wife put her foot down.

Foreman said he cried on a few occasions after retiring because he missed the big stage so much.

It took time, he said, to finally accept the fact that part of his life was over.

He’s made himself rich beyond belief selling grills and is now involved with a restaurant franchise. He’s happy at home watching his children play sports, and he’s proud of the tomatoes he carefully cares for in his garden outside Houston.

Still, there’s something missing that he can never replace.

“I’ve been successful with a lot of business things, but if I told you that took the place of boxing I’d be lying,” he said. “The thrill of a crowd roaring for you after just winning a boxing match, nothing touches that. It has to be the same for a guy dancing in the end zone or throwing touchdown passes.

“You can’t touch that with a billion-dollar paycheck.”