COOPERSTOWN — From his experience as a player to his perch as a Mets adviser, Carlos Beltrán is uniquely qualified to talk about the challenge of playing in the biggest market in baseball. 

“New York,” Beltrán said on the eve of securing baseball immortality, “is not for everybody.” 

It was for Beltrán — but only after a rough first season in Queens that provided one of the biggest tests of his career. 

It was for Jeff Kent — at least enough for the second baseman to post solid seasons with the Mets, though he did not truly take off until reaching San Francisco. 

It was for Andruw Jones — but only after a rough initial stretch in The Bronx, picking up his play enough to convince the Yankees to re-sign him for the final season of his career. 

All succeeded, to varying degrees, in New York, and all built careers legendary enough that they will be enshrined Sunday in baseball’s Hall of Fame. 

In many ways, they all are outliers, and Beltrán might now be discovering how many players never quite figure out New York.

As special assistant to David Stearns, he has watched the Mets gamble on the likes of Bo Bichette, Freddy Peralta, Luis Robert Jr., Jorge Polanco and Marcus Semien, none of whom has performed (albeit for various, debatable reasons).

It is difficult to import players from other markets, particularly small ones, and count on the talent and results to translate immediately. 

Few know this better than Beltrán, who emerged as a star in six and a half seasons with the Royals and a half season with the Astros before signing a seven-year, $119 million megadeal with the Mets in 2005. 

You know what happened next: An MVP candidate the previous two seasons was ordinary in his first with the Mets, his homers dropping from 38 in 2004 to 16 and his OPS from .915 to .744. 

“If you don’t understand the process, sometimes it could be overwhelming. For me, it was,” said Beltrán, who recovered well enough that his Hall of Fame bust will feature a Mets hat. “Coming from Kansas City, playing in New York at the beginning, I didn’t understand why the fans were getting on me. When I played in Kansas City, I never got booed. All of a sudden I’m in New York, I’m like: They booed me this whole month. 

“I’m like: Oh, my God, I just signed here for seven years and these people, they have no patience with me.” 

In those days, Beltrán said, he didn’t have anybody to guide him around the arrows and through the adversity.

He had to learn for himself how to deal with the media glare and fan expectations and jeers. 

The lessons he gained along the way he has shared with the Mets of today, including talking with Francisco Lindor before and after his rough first campaign with the Mets. 

“It’s a city where the fanbase supports their team, but at the same time they expect excellence out of the players,” said Beltrán, who also played two and a half seasons with the Yankees. “They understand the game, they know how much money you’re making, so they want you to earn every single penny.” 

His advice to those struggling to adapt? 

“You’re going to be fine,” Beltrán said. “Keep playing hard. Keep taking care of your preparation.” 

Like Beltrán, Kent said he learned plenty in New York, though Kent — who found his way to Cooperstown through the Contemporary Era committee — had to master the expectations that arrive internally and externally when being traded. 

Enjoying a strong rookie season with the Blue Jays in 1992, Kent was shipped (with Ryan Thompson) to the Mets for David Cone, who was in the middle of his second All-Star season. 

In Kent’s mind, Cone had been the Mets’ best player.

And so Kent tried to fill Cone’s shoes. 

“I just came from the American League, and so [I’m like], ‘Who cares about David Cone? I’m Jeff Kent. I’m good. I can play,’” said Kent, who sparred with teammates and heard some boos from fans after an unpopular trade. “Boy, I got beat up for that one.” 

Kent performed with the Mets, hitting 67 home runs with a .780 OPS in four and a half years before being dealt to Cleveland in 1996 in the trade that brought in Carlos Baerga and Alvaro Espinoza. 

And being shipped for Baerga tested Kent’s ego again. 

“As a player, we’re cocky and arrogant enough, we need to believe that we’re the best guy,” Kent said. “So I had that in me, but I had to tame that a little bit and use it as a tool rather than use it as a flamboyant, drama, verbal piece.” 

Jones had a shorter career in New York, spending just his twilight years of 2011-12 with the Yankees.

And even the veteran, a five-time All-Star and 10-time Gold Glove winner, needed an adjustment period. 

In 2011, Jones got off to a miserable start — 36 games into his season, he was hitting .195 with a .635 OPS — but he went on a tear beginning in mid-July, a stretch that led to the Yankees bringing him back for a final season in The Bronx and in the majors. 

Along with his other late-career stops, Jones said New York was “awesome.” 

“I have to say that New York is a great place,” Beltrán said after his words of warning. “It’s a place where you grow, you expand yourself, you get to meet so many great people. 

“I got to meet a lot of good people in the game. And I will have to say that most of the most meaningful relationships that I built in the game, I did it wearing a Mets uniform.”