In 2019, more than a decade into Lionel Messi and Cristiano Ronaldo’s rivalry, the two most famous athletes on the planet found themselves sitting next to each other in the front row of the Champions League Player of the Year awards show in Monaco. It should have been unspeakably awkward. Instead, Messi, who played for Barcelona at the time, and Ronaldo, then at Juventus, forced grins throughout the evening, turning it into a rare moment of humanity between two adversaries.

“It was curious, because we shared the stage for 15 years, me and him,” Ronaldo told an interviewer at the event, with Messi seated to his right. “I don’t know if it’s ever happened in football, the same two guys, on the same stage, all the time. It’s not easy, as you know … We’ve not had a dinner together yet, but I hope in the future.”

For most of their careers, Messi and Ronaldo either talked around their rivalry or skirted the issue entirely. Modern athletes are too smart and too media-savvy to publicly admit personal grudges anymore. That interview was the first time either of them had explicitly acknowledged the competition that fed the multi-billion-dollar football industry, and one that came to define an era of the world’s most popular sport.

Both in their mid-30s, twilight years for athletes, they could at last publicly recognize their competition. More than that, the exchange hinted at something else—something we also discovered in writing our book about the intertwined stories and legacies of these two men.

Modern athletes are too smart and too media-savvy to publicly admit personal grudges anymore.

For a long time, the Messi-Ronaldo rivalry was portrayed as a story of the extraordinary differences between two greats. One is small, one is big. One likes to weave past defenders, one likes to burst past them. One is shy and humble, the other is a strutting peacock. If you know anything about international soccer, you already know that Messi is the former and Ronaldo the latter.

Those contrasts help explain why this rivalry has generated so much energy and zeal in otherwise rational people. For millions of fans around the world, “Messi or Ronaldo?” isn’t simply a barroom argument or affirmation of fandom but something closer to a statement of philosophy, of values, of how you view the world.

The truth, however, is that beyond the cartoonish differences, Messi and Ronaldo have more in common as players and as people than anyone was willing to admit for most of their careers. Fans are suckers for a narrative that characterizes them as polar opposites. Yet the more we researched their stories, and the longer their careers have gone on, the more similar they have started to seem.

There is no such thing as a low-maintenance genius. Messi is portrayed as the humble hero, the ultimate team player, and the guy who shunned stardom to be remembered as a decent guy instead of a soccer great. But executives, coaches, and players who have been around Messi told us he can be completely impossible.

For instance, when he started playing for Paris Saint-Germain last year, he demanded to keep his Barcelona jersey number, 30, which the French league reserved for goalkeepers. After Messi refused to change, they amended the rules to keep him happy.

Ronaldo, meanwhile, is cast as the preening superman, an advertising billboard in aviator shades, the guy who always seems mildly annoyed by the presence of his own teammates. Yet, many of those who have coached or played alongside him describe an approachable character with just-one-of-the-guys humility. When Weston McKennie moved from the U.S. national team to Juventus, he says Ronaldo took him under his wing in Italy, offering advice on techniques, nutrition, and post-game recovery.

Contrary to public perception, Messi and Ronaldo are two expressions of the same merciless drive, a physical and psychological need for perfection. It’s their similarities, not their differences, that make it so difficult to weigh up one without the other.

“They dominated at the same time, with crazy stats and albeit different styles,” says Pascal Ferré, who oversees the Ballon d’Or, the annual award for the world’s best player, which Messi and Ronaldo have held a combined 12 times.

“In the grand scheme of history, you almost have to consider them as one player.”

Jonathan Clegg and Joshua Robinson are both editors for The Wall Street Journal. Their book Messi vs. Ronaldo: One Rivalry, Two GOATs, and the Era That Remade the World’s Game will be published on November 1 by Mariner