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.