MESA, ARIZONA— A year ago, as the promising young Chicago Cubs prepared for the 2016 season, the only cloud that hung over their training camp was the palpable weight of a hundred and eight years of futility. Though management, coaches, and players cheekily denied it, The Curse was a brooding and inescapable presence. Could these Cubs, torn down and rebuilt over several dreadful seasons, overcome the most prodigious title drought in the history of professional sports?

They answered that question last fall, with a pulsating, extra-inning victory over the Cleveland Indians in Game 7 of the World Series, a cinematic ending as improbable—and therefore appropriate—as the horrific streak itself. Now the World Champs have returned from their short, celebratory winter to even greater expectations but a more conventional historical barrier. No team has won consecutive World Series championships since the New York Yankees completed a three-peat in 2000. No National League team has accomplished this feat since the legendary Big Red Machine of Cincinnati, forty years ago.

Theo Epstein, the Cubs’ president of baseball operations, knows the history and the numbers. “If you’re a lousy team, you start the season with about a three per cent chance of winning the World Series. If you’re a great team, your chances are about twelve per cent,” Epstein told me as we stood on the balcony of the Under Armour Performance Center, the team’s training facility, watching the players go through morning calisthenics on a field below. “It’s just really hard to win the World Series.”

Epstein’s obsession with data is well known. As the twenty-something general manager of the Red Sox, he was one of the early pioneers of the “Moneyball” era, and used big data to unlock hidden truths about the game, a strategy that helped lead Boston to two championships. Year by year, he has refined and expanded that quest, perpetually driving his like-minded young collaborators and a war room of analytics geeks for new insights about how to scout players and win games. And he’s had to, because the rest of the league has caught on. Analytics have offered upstart and underfunded franchises the tools with which to maximize their chances. “It used to be the rich teams like the Yankees could load up on talent and dominate. Now low-budget franchises are more competitive,” the pitcher Jon Lester told me as he prepared for his day’s workout regimen in the Cubs’ spring clubhouse. “It’s just harder to win consistently than it used to be.”

Lester knows intimately the challenges of repeating as champions. Originally drafted by Epstein in Boston, the tall, stoic left-hander was a mainstay of two championship Red Sox teams. When the Cubs began to show signs of competitiveness, in 2014, Epstein recruited his old ace, a free agent, with a six-year, hundred-and-fifty-five-million-dollar deal to anchor Chicago’s pitching staff. Last year, Lester won nineteen games and played the critical, steadying role that Epstein envisioned for him in the playoffs and World Series, despite a strange and inexplicable mental block against throwing the ball to first base.

On paper, the 2017 Cubs should be even better than the curse-busting crew of a year ago. The heart and soul of the team are young stars who have not yet reached their prime on baseball’s actuarial tables. The third baseman Kris Bryant, who won the Rookie of the Year award in 2015, and is the reigning league M.V.P., turned twenty-five in January. Addison Russell, the elegant All-Star shortstop, is just twenty-three. Javier Báez, an ebullient infielder whose prestidigitation in the field and thunderous bat helped ignite the Cubs during last year’s playoff, is twenty-four. The first baseman Anthony Rizzo, the team’s emotional leader and longest-tenured Cub, is all of twenty-seven.

PHOTOGRAPH BY ROB TRINGALI / GETTY Photograph by Rob Tringali/Getty

And then there is Kyle Schwarber, twenty-four, a four-by-four truck sprung to life as a preternatural hitter of baseballs. Schwarber missed almost the entire 2016 season with a knee injury, only to return for the World Series—three months before doctors said he would be ready—and emerge as one of the hitting heroes. “Whenever you talk to this young man, look in his eyes,” the team’s manager, Joe Maddon, told me as we sat in his cramped, windowless office in Mesa. “Maybe one, two per cent of all Major League baseball players could have done what he did last year. Maybe just one guy could have. It might have just been one. He’s just a different cat.”

The only discernible chink in the Cubs’ armor is an aging corps of starting pitchers. Lester is thirty-three. John Lackey is thirty-eight. And Jake Arrieta is thirty-one. Of the top four starters, only Kyle Hendricks, at twenty-seven, would be considered young by baseball standards. Behind them are several journeymen who have been auditioning for the fifth starting spot. The Cubs’ league-best pitching staff was remarkably healthy and consistent last year. Epstein acknowledges that this run of luck cannot be counted on again. “If one of our pitchers goes down, we just don’t have the same depth we do with position players,” he told me, suggesting that he might be forced to barter some of his prized minor-league prospects for more pitching later this year.

Beyond the hazards of injury and the competitiveness of the league, there are other obstacles to repeat success. When you win the World Series, your off-season is shortened by more than a month, leaving players less time to regenerate for the next campaign. Any winning team is showered with attention during the interregnum—oftentimes one long party, which can swell the head and the body. Finally, while the desire to win may still be there after securing the title, the same level of commitment may not. “The thing that often stops teams from repeating are the internal dynamics that crop up after you win—jealousies, rivalries, guys feeling like they didn’t get the credit they deserve,” Bruce Levine, a veteran baseball writer who has covered the Chicago teams for three decades, said. “I have seen very little of that with this bunch. They’re a high-character group. They’re young, but they’re very professional. From the stars to the bench guys, they feel a responsibility to each other and their shared goals. It’s very unusual.”

It is unusual but not accidental. Alongside all the sophisticated data analysis and neuro-testing that Epstein and his collaborators have marshalled to evaluate talent, they have deployed batteries of psychological testing and demanded that scouts investigate the background and character of prospective draftees. Often, Epstein, whose twin brother, Paul, is a social worker, will interview the top player candidates to get his own feel for them as people and potential teammates.

“I came into the game thinking that all the touchy-feely stuff about chemistry and connection was just sort of a manufactured narrative, and that, ultimately, talent wins, and you can see it on paper why clubs win,” Epstein told me when I asked about the personality of his team. “With each year, you realize that the connections in the clubhouse, the character of the guys, the feeling, the ability to come together as a team affects the performance, so that affects the stat lines and what you see on paper, too. It’s an important part of it.”

Last year’s championship team was memorable as much for its character and cohesiveness in the clutch as for its considerable athletic prowess. “Because they were such great teammates and they cared about each other and they put their own self-interest behind the interest of the team and supported one another, the whole became greater than the sum of the parts, and they were able to elevate each other and accomplish something special,” Epstein told me, kvelling about his men.