(CNN) On Sunday, Tom Brady un-retired.
"These past two months I've realized my place is still on the field and not in the stands," the NFL quarterback tweeted to his 2.5 million Twitter followers. "That time will come. But it's not now."
What Brady didn't say -- but undoubtedly meant -- is that even after being away from the game for only a short time, he missed it. Badly.
He's far from the only top-tier athlete to reconsider retirement. There's Michael Jordan, Muhammad Ali, Mario Lemieux, Lance Armstrong and Brett Favre -- several times!
All of those athletes didn't un-retire for exactly the same reasons. But there is a common thread that connects all of them: They were addicted to the competition and simply couldn't find it in other pastimes in their lives.
That addiction to competition runs through another profession: politics. And it's why so many elected officials just can't seem to quit running.
"A man stung by the presidential bee contracts an incurable disease that only embalming fluid can cure," said Harold L. Ickes, who was secretary of the Interior for more than a decade during the presidency of Franklin D. Roosevelt. (Ickes is the father of Harold M. Ickes, the longtime confidant of the Clintons.)
Ickes was talking, specifically, about Thomas Dewey, who was the Republican nominee for president in 1944 and 1948. He lost the first race in a landslide to Roosevelt. The second race was so close that some newspapers -- most notably the Chicago Tribune -- declared Dewey the winner, only to see Harry Truman eventually emerge triumphant.
Dewey was hardly the only politician who just couldn't quit running for president.
Adlai Stevenson II was the Democratic presidential nominee in 1952 and won a contentious convention fight for the nod in 1956. He ran a third time for the job in 1960, but was defeated by John F. Kennedy.
Hubert Humphrey, a senator and onetime vice president, ran unsuccessfully for president three times: 1952, 1960 and 1968. (He was the Democratic nominee only once -- in 1968 -- when he lost to Richard Nixon.)
Ronald Reagan, the father of the modern Republican Party, ran for president in 1968 and 1976 before finally winning in 1980.
Hillary Clinton ran for president in 2008 and 2016, losing both times. (She also seriously considered running in 2004.)
Mitt Romney lost a bid for the Republican presidential nomination in 2008, won the nomination in 2012 and was mentioned as a 2016 candidate before deciding against a third bid.
And let's not forget that the current occupant of the White House -- Joe Biden -- lost bids for president in 1988 and 2008 before winning the Democratic nomination and the general election in 2020.
I'm in the midst of writing a book about the sports presidents played, loved and spectated -- and what those sports reveal about who they are, really, and how they governed.
The trait that has come up again and again in my research is that presidents are among the most competitive people on the planet.
"He is the most competitive person," said David Katz, a frequent golfing partner of former President Barack Obama. "He loved the competition of the game and the moment. It was almost like a political race."
I'd disagree only slightly with Katz. It wasn't "almost" like a political race. It was exactly like a political race.
The simple reality is that extremely competitive people tend to find fields in which they can be routinely tested against others to see how and if they measure up. For athletes, that competition itch is scratched through practices and games. For politicians, it's through primary and general elections.
And what they often come to realize is that the competition high produced in the heat of a game or a campaign can't be replicated. They wind up chasing that feeling for the rest of their lives -- even when the chances of winning appear elusive.
That's the feeling Brady is chasing. "Unfinished business," he said by way of explaining his return to the Tampa Bay Buccaneers. Joe Biden understands.