BOSTON — It’s been more than three years since the Brooklyn Nets mortgaged their future in a trade with the Boston Celtics for Paul Pierce and Kevin Garnett, and they still can’t escape it. They’ve tumbled downhill ever since, from 49 wins in 2012-13 to a rock-bottom 21 last season.

Garnett, 40, is retired, and a 39-year-old Pierce is on the verge of joining him. Brook Lopez is the only current member of the Nets who was even on the roster when Billy King pulled the trigger on that deal. King is gone, too, and Brooklyn is on its fourth head coach since the trade.

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The aftershocks can still be felt in Brooklyn. Boston received three unprotected first-round picks from the Nets and the right to swap another. While the first of those, James Young, barely made the Celtics this season, the second went No. 3 overall this past June. Given prognostications, the pick swap and Brooklyn’s first-round pick in 2018 both have a chance to be No. 1 overall.

“I was fully aware,” Kenny Atkinson, whose vibe is sincere, business-like and “don’t you dare mess with me” all at the same time, said when asked if he considered Brooklyn’s future draft status upon accepting his first NBA head coaching position in April. “I understand the situation.”

Making matters worse, Atkinson debuted on the road opposite the Celtics on Wednesday night, and rookie Jaylen Brown, who came courtesy of Brooklyn with that third overall pick, beat Nets guard Joe Harris backdoor for an uncontested dunk that gave Boston a 22-point lead with 9:37 remaining in the fourth quarter. And three years of jokes about the Nets ineptitude came to life.

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“We don’t talk about projections,” Atkinson said pregame. “We don’t talk about win shares. We don’t talk about it. It’s a cliche, but we’re so focused on the process, so focused on our team, so focused on team development and player development, and we’re going to measure those.

“But, that being said, we’re competitors. All of us, all of those guys in the room, they’re coming in here to get a win, so all those long-term projections and building and all that goes out the window. When that ball’s tipped up, we’re going to compete as hard as we can to win the game.”

But even for those on the Nets who tried desperately to avoid criticism of the team this summer, the sheer amount of Brooklyn bashing made it impossible. A sampling of those prognostications:

While many season previews lauded new Nets general manager Sean Marks for, as our own Dan Devine put it, “tearing the roster down to the studs and starting the process of building for the future,” a consensus picked Brooklyn to finish at, or just above, the bottom of the standings.

“We don’t pay attention,” Lopez insisted. “I don’t read that stuff. I know other people don’t. We’re focused on ourselves. We’re confident on what we’re doing, and we’re trying to build that up.”

If you vacationed in Las Vegas this offseason, the desert provided no oasis. The Westgate SuperBook set Brooklyn’s over/under for wins at 20.5 — four fewer than the next-closest team, the Los Angeles Lakers, who somehow won fewer games (17) than the Nets in 2015-16, but added second overall pick Brandon Ingram and a couple bigger-name free agents to the mix.

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In the visitors’ locker room at TD Garden prior to the season opener, an injured Randy Foye and a stretching Harris carried on a conversation in one corner. Elsewhere, Nets employees joked about the least in-shape player on last year’s 21-win team — one who prioritized smoking cigarettes over working out and actually started for the team at one point. Meanwhile, Chris McCullough sat alone in his stall, staring intently at a preseason Celtics-Nets game on the TV.

The Nets picked McCullough with the No. 29 selection in the 2015 NBA Draft, because King had given the Atlanta Hawks the right to swap picks in exchange for Joe Johnson back in 2012. Along with Rondae Hollis-Jefferson, taken six picks earlier, McCullough represented Brooklyn’s first opening-round picks since the draft-night trade for Garnett and Pierce two years before.

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Clearly tired of answering questions about the team’s absence of expectations since his arrival, McCullough conceded, as hard as he’s tried to tune out the noise, the chatter is unavoidable.

“They’re young guys. I’m sure [they hear it],” Atkinson said of season-long projections before the opener. “I know I don’t look at it. I don’t look at it. I try to shut that out and, again, focus on our guys and our development, and I hope they do the same. I really do, because we’re not putting newspaper articles up in the locker room. I think these guys are professionals. They know what they have to do, and they know what it takes to get better and for this team to get better.”

Indeed, guys like McCullough shouldn’t care about how many wins some bookie or analytics guy projects for the Nets. On a team like Brooklyn, they’re more concerned with keeping an NBA job, taking advantage of the opportunities they’re given and cashing in when their current contracts come to a close. The challenge for Atkinson comes in harnessing that energy on a roster featuring eight guys born in the 1990s. If there’s hope of establishing a winning culture and conquering the mountain, they must band together. Nobody can push that rock uphill alone.

“We’ve got to tell them you guys are obviously writing from an outside perspective, and you’re not in the locker room all the time,” Lopez, 28, said of advising younger players. “You don’t know what’s going on. You don’t know what we’ve been through, and we let them know to have that confidence and let them know we can do something, because that’s completely necessary.”

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These Nets are in the strangest of positions, with the longest of odds to win in the now and no reason to tank for the future. They’re in limbo, destined to live out 82 games in NBA purgatory. Players can either rage against those projections united and keep pushing the rock upward as a unit or let doubt seep into the cracks and splinter everything until it all comes crashing down.

After whiffing on attempts to sign Tyler Johnson and Allen Crabbe for a combined $125 million this summer, when the Miami Heat and Portland Trail Blazers respectively matched their offer sheets, Brooklyn’s brass was left with only one approach to the season: maintain cap flexibility, develop the current crop of players in hopes of building rotational depth, and try like hell to exceed expectations and become an attractive destination for next year’s crop of free agents.

With that in mind, new Nets GM Sean Marks targeted competitive players with plenty to prove on short-term deals. He brought Jeremy Lin back to New York in hopes of capturing Linsanity in a bottle again. He gave Anthony Bennett one more shot to prove he’s worthy of his No. 1 overall selection in 2013. He added respected vets Trevor Booker, Luis Scola, Greivis Vasquez and Randy Foye to help instill accountability. And he took a flier on former Philadelphia 76ers second-round pick Justin Hamilton, who answered with 19 points and 10 boards in the opener.

“Sean did a great job bringing in a group that’s fun to coach and that’s going to compete,” Atkinson said of a team that features 10 new faces, “so that’s what we’re focused on right now.”

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The roster-tearing-down and roster-building efforts by Marks have been covered ad nauseum, but there is no escaping the dark cloud that fills the void left by those next two first-round picks. Lottery picks offer hope for fans and front offices in the rebuilding process, and the absence of them leaves the Brooklyn faithful in a state of despair. But for free agents like Hamilton and Lin, who saw the Nets as an opportunity to reclaim their careers, those picks are of little concern.

“That’s a management thing,” said Hamilton, who’s on his sixth NBA roster — and 10th team — in five years. “For us, it’s just getting better and winning and trying to perform at the highest level for Kenny and those guys, because they put the trust in us, and we want to produce for them. … There’s a lot of experience in here. You go from being on top teams to low teams, and you just have to have a mentality, and the mentality for us is just to get better every day.”

Meanwhile, Marks continues to clean up the mess King made. He’s cleared enough cap space to offer two max contracts in 2017 and could clear even more with the right deal for Lopez, who was left out of the starting lineup in the second half against Boston, a move Atkinson revealed afterward to be a season-long effort to limit his center’s minutes. Such a trade might also fetch a first-round pick. In the meantime, the Nets are comfortable with Lopez as a potentially devastating pick-and-roll partner for Lin, and area hipsters can revel in the Brook-Lin pun.

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Brown’s aforementioned dunk forced an Atkinson timeout, but the damage was done. As Boston’s lead continued to hover between 17 and 23 and the clock crept past the halfway point of the fourth quarter, the Nets waived the proverbial white flag, inserting McCullough and 2016 second-round pick Isaiah Whitehead for their first action of the regular season with 3:57 left.

And in that moment, of all moments, Brooklyn discovered its identity, achieving everything Atkinson’s preached throughout the preseason about embracing the climb with perseverance. Keep pushing that rock up the hill, even if everyone expects it to come crashing down again.

McCullough converted a floater 20 seconds into his stint against the Celtics. The end of the bench on a roster everyone wrote off before the season started got four straight stops and answered with a flurry of baskets, cutting Boston’s lead to single digits and forcing Brad Stevens to reinsert his starting lineup. Meanwhile, Atkinson stuck with his reserves, and they responded with another 7-2 run that slashed a 23-point deficit down to three with 46 seconds remaining.

“Did I expect it to be a three-point game with 46 seconds left? No, I didn’t,” said Lin. “But that’s what happens when you play the right way and you play hard. That’s the game of basketball. I’ll be honest, starting with me, I want to be able to bring that effort on Friday the way they did the last five minutes of the game. That was inspiring, and I’m not even joking. That was inspiring.”

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The Nets got two good looks to tie the game, including one by Hamilton on an after-timeout play that just missed from the corner. A pair of Isaiah Thomas free throws on the other end all but sealed the game for the Celtics, but everyone left understanding these Nets are on the ascend.

“It’s just a matter of getting better,” said Hamilton. “We’ve said it the whole preseason. We’re trying to establish a system, a program that’s committed to getting better, committed to working hard, and so for us it’s every day trying to get better. Tonight, there was moments where we had lapses, and then when those guys came in, we just preached defense, try to get better, try to get better, and that helped us at the end make that run. So, I think for us it’s just a matter of every day we’re going to work, regardless of the outcome, and if we work our best, we’ll win games.”

Come Friday, that work resulted in a 103-94 home victory against the Indiana Pacers, another projected challenger in the East. The Nets got 25 points from Lopez, a 21-9-9 from Lin, a double-double from Booker and 18 points off the bench from former D-Leaguer Sean Kilpatrick.

“I thought Brooklyn came out and played harder than we did,” Pacers coach Nate McMillan told reporters after his team’s first loss of the season. “They’re cuts were harder offensively, and defensively they really got out and got after us, denying and pressuring. They play with a sense of urgency that we talked about, that we need every single night. I thought we had that in the first game. Tonight, we did not have that energy, and they played harder for 48 minutes.”

Some 24 hours later, in Milwaukee for the second night of a back-to-back, the Nets erased another double-digit lead after the half, only to fall victim to Bucks big man John Henson’s tip-in at the buzzer for a 110-108 final. With Lopez sitting the entire game, Booker logged another monster double-double, and Bojan Bogdanovic scored 12 of his 26 points in the fourth quarter.

If we’ve learned anything from Brooklyn’s first three games, it’s that these Nets won’t back down. And their competitiveness might be the surprise of the season so far. The team that has nothing to lose by pushing forward and everything to lose by falling backward is climbing the hill.

***

Marks comes from the Gregg Popovich school of basketball, having served as an assistant on the San Antonio Spurs staff from 2013-16. Popovich’s philosophy, borrowed from “The Stonecutter’s Credo,” written by late 19th century muckraking journalist Jacob Riis, is thus:

“When nothing seems to help, I go and look at a stonecutter hammering away at his rock perhaps a hundred times without as much as a crack showing in it. Yet at the hundred and first blow it will split in two, and I know it was not that blow that did it — but all that had gone before.”

But Brooklyn’s rebuild isn’t so much about the reps as it is an ascent from the bottom, so the Greek myth of Sisyphus is more apropos for the Nets, at least this season. Even if the odds of reaching the NBA mountaintop are impossible in 2016-17, they’ll drive themselves crazy if they don’t embrace the task of pushing that rock on the climb, regardless of any predictable outcome.

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“I’m not even sure what the outside projections are that much, to be honest,” said Lin, a former D-Leaguer himself. “I know we’re not high. I know I’ve had friends who’ve said, ‘Oh, they picked you last or close to last,’ or whatever. Beyond that, I don’t really know the specifics of it. But my whole life, if I just looked at the odds of everything, I wouldn’t be here, so I don’t really care what they say, and I just care about us getting better in here, us sticking together, playing the right way, and then the wins will take care of itself. Whether they’re right or whatever, I’m good.”

Pushing that boulder can be easier than looking beyond it and seeing how far there is left to go. As another great philosopher, Miley Cyrus, once said, “There’s always gonna be another mountain. I’m always gonna wanna make it move; always gonna be an uphill battle. Sometimes I’m gonna have to lose. Ain’t about how fast I get there, ain’t about what’s waitin’ on the other side. It’s the climb.” So, the Nets begin their ascent, even if the 2016-17 campaign could be a futile exercise.

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Ben Rohrbach is a contributor for Ball Don’t Lie and Shutdown Corner on Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach