(CNN) -- George Bernard Shaw is said to have once written, "Progress is impossible without change, and those who cannot change their minds cannot change anything."
There's no doubting ol' George would be drubbed as a "flip-flopper" if he were to set foot in a modern political campaign (after denying he ever said that, of course).
But humans must think there's something to it. We've been changing our minds forever, right?
So, lest Ohio Sen. Rob Portman think he's out there on his own in deciding he was wrong about gay marriage, here are a few examples of some famous changes of heart, both real and imagined:
Bill Clinton: From Burger-Eater-in-Chief to Vegan
From French fries to fried chicken, the former president's appetite was legendary. White House pastry chef Roland Mesnier had another world for it, he told Washingtonian magazine: "Scary."
"He had a big appetite, scary," the magazine quoted Mesnier as saying. "He could eat five or six pork chops."
He loved the food at the White House so much, in fact, he gained 18 pounds between 1997 and 1999.
But a few years ago, Clinton went almost entirely vegan after two bouts of heart surgery. No more cheeseburgers, no milkshakes. No eggs.
"I essentially concluded that I had played Russian roulette," Clinton told CNN's Dr. Sanjay Gupta in 2011.
"I was lucky I did not die of a heart attack," he said.
That nameless hater of green eggs and ham
He does not like them, Sam-I-am. That's what the shaggy, black-hatted thing in Dr. Seuss' legendary childrens' book tells hardcore ham-and- enthusiast Sam-I-Am. Finally, worn down by Sam-I-Am's relentless badgering, the creature -- worn down -- finally relents. "If you will let me be, I will try them, you will see."
A bit of munching, then ... "Say, I like green eggs and ham! I do! I like them Sam-I-Am!"
The same cannot, unfortunately, be said of the millions of children whose well-meaning parents have invoked Sam to get their children to eat vegetables.
They still won't eat them. Not even on a goat.
Brett Favre: I'm retired. No I'm not. I'm retired. No I'm not
In 2008, the Green Bay Packers quarterback decided to call it a career after 17 seasons, saying he'd had a good run but that "all good things must come to an end."
"I know I can play, but I don't think I want to," he told reporters.
But within a month, he'd had a change of heart and said he wanted to come back.
Then he didn't.
Then he wanted back in.
The Packers, exasperated, finally offered Favre a contract just to agree to stay retired. He refused and was eventually traded to the New York Jets, where he played for a season, then retired.
Until he had a change of heart and came back to play for the Minnesota Vikings. An ankle injury ended that comeback.
As of this writing, at least, the future Hall of Famer is still retired.
Ebenezer Scrooge: After sleeping on it ...
When the world first met Ebenezer Scrooge in 1843, it was as a miserly skinflint whose tightwad ways made him a virtual ghost among the merrymaking men and women of Victorian London. He was uncaring to the concerns of others that he'd just as well see the poor die off to, as he would say, "decrease the surplus population."
But, after a series of spectral visits in which he is shown Christmases past and present and learns of the dismal fate awaiting him in death, author Charles Dickens has his Scrooge awake a new man, throwing money around as if it were candy and making as merry as he could for the rest of his days.
"And it was always said of him," Dickens wrote in the last paragraph of his novel, "that he knew how to keep Christmas well, if any man alive possessed the knowledge."
The Apostle Paul: From scourge to saint
As the New Testament tells it, Saul of Tarsus was bad news for early Christians.
Acts of the Apostles describes him "breathing threats and murder against the disciples of the Lord."
But one day, as he traveled to arrest Christians in Damascus, Saul reported seeing lights and hearing the voice of Jesus Christ asking, "Saul, Saul, why do you persecute me?"
He took the name Paul and became the most significant evangelist of the early church.
It's from this biblical story that we get the phrase "Damascus road experience," describing a profound change of heart.
Scientists: Sorry, Pluto, you're off the team
Back in 1930, the scientists who thought about such things decided a newly discovered thing way out in the distant solar system was a planet, and decided to name it Pluto.
But little Pluto didn't even get through one of its 248-year trips around the sun before Earth's scientists changed their mind.
A mere 76 years after earthlings first spied the planet in the black of space, they changed their collective minds. Too small, the scientists said. Too erratic. We found something bigger farther out. Heck, Pluto's only twice as big as its moon!
It's certainly not the only time scientists have changed their minds. But it's one that's captured plenty of the public's imagination.
How many planets (or, certainly, ex-planets) have their own fan site?