Talk of Billy Beane’s legacy surfaces a lot these days. It’s picked apart, debated and examined at all ends of the baseball world, and it’s usually a very simple equation. It goes something like this:

Win a Division Series, it’s intact. Win a World Series, it’s cemented. Lose a wild-card game, it’s mud.

It might be a premature way of deciding what a 52-year-old will be remembered for, someone who not only has a contract through 2019 as A’s general manager but owns part of the team.

But that’s the price of messing with a good thing.

Which, in retrospect, wasn’t that good, Beane says now.

“Simply put,” he said Wednesday in manager Bob Melvin’s Coliseum office, “if we don’t have Jon Lester, I don’t think we make the playoffs.”

As bold a statement as the Yoenis Céspedes-for-Lester trade itself.

The 2014 A’s season went down in flames Tuesday night in Kansas City, and Beane was left to explain a day later what went wrong. A team that went from dominant to docile at about the time Beane traded Céspedes to Boston lost 9-8 in a painful season-ending wild-card game.

“One thing I’m going to say right now,” Beane said amid a round of questions on the Céspedes-for-Lester trade, “the Angels were going to catch us. They played nearly .700 ball from a certain point on.”

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Indeed, Beane had warned about the Angels in conference calls following his Fourth of July trade for starters Jeff Samardzija and Jason Hammel from the Cubs and July 31 deal for Lester. He had denied the deals were about finally escaping the first round and getting deep into the playoffs, saying they were about winning the division.

But no way could he have imagined the A’s finishing the season 16-30 — or all the injuries and slumps — and he’d challenge anyone bringing up the if-it-ain’t-broke-don’t-fix-it argument, saying, “What I didn’t reveal (on the conference calls) is, I was also concerned about us. It’s not where you are, it’s where you’re headed.”

Beane saw the A’s were on the verge of breaking, and one of the examples he cited was Jesse Chavez, who was thrust into the rotation because of Jarrod Parker’s and A.J. Griffin’s Tommy John surgeries but wasn’t expected to last over the long haul after pitching extremely well early.

For the record, Melvin never imagined the Angels running away from the A’s, until it happened. Then again, that’s part of a manager’s DNA.

“I look at it differently. (Beane) is a big-picture guy. I’m grinding on the day,” said Melvin, who spoke with reporters after Beane’s session. “As poorly as we were playing and as well as they were playing, even when they passed us, I thought we’d be able to catch them again based on the games we had. I probably look at it differently than a wider perspective.”

In any event, Céspedes’ absence was felt throughout the clubhouse, players admitted Wednesday.

“You’re going to miss somebody like that no matter what,” Josh Reddick said while packing bags at his locker, “especially when you’re used to having him in there for so long protecting so many guys. He’s in a pretty good set-up over there in Boston right now. He should be happy. He’s hitting in front of or behind Big Papi (David Ortiz) and Mike Napoli.

“We definitely struggled with it for it a little while. It’s how you handle it. We just didn’t handle it the best we could. We couldn’t find the right person at the right time to fill in.”

Like Reddick, Jed Lowrie wouldn’t blame the A’s collapse on the Céspedes trade. But Lowrie did suggest the roster shuffling affected team chemistry.

“It’s the reality,” he said. “When you take a few guys out of the clubhouse and add a handful of new guys, as much as people don’t think it’s a big deal and we’re all professionals out here playing a game, there’s something to chemistry and having an identity as a team and an offense.”

That doesn’t register with Beane, who said, “I think production ultimately creates chemistry.”

Beane mortgaged 2015 to win big in 2014, not only dealing Céspedes but also promising shortstop Addison Russell. Now, the A’s will be in the market for a right-handed hitter (which they had in Céspedes) and, if they don’t re-sign Lowrie, a shortstop (which they would have had in Russell).

Beane’s shuffling was a huge gamble that can be seen as a detriment or a benefit. No one knows if the A’s would have performed better with Céspedes instead of Lester, who was by far the best starter the final two months. While he pitched his worst A’s game Tuesday, he also pitched into the eighth inning with a four-run lead.

This story won’t end. Nor will the talk of Beane’s legacy. He’s OK with that. He can feel proud about designing teams that reached the postseason three straight years with a relatively small payroll and a lot of turnover.

Beane said goodbye to Lester and other players, “half of them I won’t see again. It’s not like across the bay, where it’s, 'Hey, we’ll see you all the next five years.’ ”

With that, the interview ended. But not before the question of his legacy came up.

“My legacy,” he said, “is my kids. Truly.”

John Shea is a San Francisco Chronicle staff writer. E-mail: jshea@sfchronicle.com. Twitter @JohnSheaHey.