The Nets were expecting to vie for N.B.A. championships, and perhaps some day they will. But that day is not now, and another abbreviated postseason appearance ended on Monday when the Boston Celtics defeated them, 116-112, to complete a four-game sweep in their first-round playoff series.

It was a fitting finale to a disjointed season for the seventh-seeded Nets, who spent months cycling through a motley cast of characters. They were undone by injuries and absences, by a mishmash roster that could not unearth a coherent brand of basketball, and, finally, by a superior opponent that put its suffocating clamps on two of the planet’s best players.

The Celtics produced the league’s top-ranked defense in the regular season, and they proved it was no fluke against Kevin Durant and Kyrie Irving. Ime Udoka, the Celtics’ first-year coach, was one of Coach Steve Nash’s assistants in Brooklyn last season, and he applied his institutional knowledge throughout the series.

Next up for the second-seeded Celtics is the winner of the first-round series between the Chicago Bulls and the Milwaukee Bucks. The defending champion Bucks have a three-games-to-one lead entering Game 5 of their series on Wednesday.

The Nets, who had the second-highest payroll in the league this season, will try to recalibrate. Nash, who was hired by the Nets in 2020 without any head coaching experience, has now presided over two early postseason exits. (The Nets lost to the Bucks in the Eastern Conference semifinals last season.) Irving, who can become an unrestricted free agent, has said that he intends to re-sign with the team. But he appeared in only 29 regular-season games this season because of his refusal to be vaccinated against the coronavirus.

The season was also interrupted by a midseason trade with the Philadelphia 76ers, who acquired James Harden in exchange for a package that included Ben Simmons, Seth Curry and draft picks. Simmons arrived in Brooklyn with a balky back and said he had been dealing with mental health issues for months. He never appeared in uniform.

As for the Harden experiment, it was a bust. Harden, Durant and Irving played together in just 16 games over two seasons, including the playoffs.

Before Game 4, Nash reflected on the Nets’ tumultuous season and spun it forward, saying it had made the team “better” and “stronger.”

“We took the challenge and we all grew from it,” he said. “And at some point, those challenges will afford us a lot. We hope that we don’t have to face so many going forward, though.”

Durant missed 21 games after spraining his knee in January, then played heavy minutes late in the regular season as the team scrambled for a spot in the play-in tournament. After Durant attempted just 11 field goals against the Celtics in Game 3, Nash acknowledged that fatigue may have played a role.

“Kevin’s had to play 40-plus minutes for five-plus weeks after missing six, seven weeks,” he said, adding, “I’m sure that’s taken a big toll.”

And there were the team’s highly publicized absences. Simmons watched the first three games of the series from the bench in street clothes. Harden now plays in Philadelphia. And Joe Harris, one of the team’s best shooters, had a bone particle removed from his left ankle in November. When his rehabilitation had a setback, he underwent another surgical procedure in March that ended his season.

Against the Celtics, the Nets missed Harris’s length on defense along with his ability to stretch the floor as a 3-point threat. As a result, the Celtics could be even more aggressive about sticking multiple defenders on Durant whenever he touched the ball.

The series itself was a swift descent into futility. After the Celtics’ Jayson Tatum won Game 1 with a buzzer-beating layup, Irving used several profanities to describe his interactions with fans who were sitting courtside in Boston. (The N.B.A. subsequently fined Irving $50,000 for making obscene gestures.) After the Nets got thumped in Game 2, Irving heaped praise on the Celtics’ young core, telling reporters that “their time is now.” And after he struggled in Game 3, Durant sounded baffled at his postgame news conference. What could he possibly do to keep the series alive? He did not have any immediate solutions.

“Maybe shoot more, maybe be smarter,” he said in a slow monotone. “Catch the ball closer to the rim. Play faster. Catch and shoot more.”

Durant said he would try to “figure it out” by studying more film ahead of Game 4.

Now, the Nets have an entire summer to search for answers.