The game was over, and the crowd at Barclays Center was chanting “M-V-P.” The fans wore N.B.A. jerseys in all of the team’s colors, and their star raised his arms to acknowledge their praise.

But Kyrie Irving was already headed to the locker room. So, too, was Kevin Durant. Ben Simmons wasn’t even in the building. This was not a celebration for the Nets, who play their home games here. It was for the Boston Celtics, for their star Jayson Tatum and for the team that had just accomplished a once-unthinkable feat: a four-game sweep of the Nets in the first round of the playoffs. The Nets superteam the Celtics faced, built around Irving and Durant to win a championship in June, didn’t even make it to May.

It was a dismal scene to end a season that started with outsize expectations in October. The Nets had three of the best players on the planet, a cast of characters that was the N.B.A.’s version of “Ocean’s Eleven.” Team executives around the league feared them. In fact, in a preseason poll by NBA.com, 72 percent of the league’s general managers predicted that the Nets would win the title. The Los Angeles Lakers finished second, with 17 percent of the vote, proving that nobody knew much of anything: The Lakers did not make the playoffs at all.

Yet when the season started, there was a big question: What could prevent those two teams from meeting in the N.B.A. finals? Who else but LeBron James could possibly stop Durant from delivering the Nets their first N.B.A. title? And who besides Durant could impede James’s march to a fifth championship?

It turned out, plenty would get in their way.

The Nets and the Lakers failed — spectacularly — at creating successful superteams, though the failures had different roots. For the Nets, it was a mix of the absurd: a star who wouldn’t get vaccinated against the coronavirus; another star who wanted out after forcing his way to the Nets in the first place; a replacement star who didn’t even show up for the elimination game.

For the Lakers, it was pure Hollywood: an aging former All-Star who wanted the ball for himself when his coach wanted him to share; a crew of has-beens hoping for one last hurrah; the A-list star trying to carry the team, but unable to do it the way he had so many times before. Young opponents laughed at them, openly, and reveled in precipitating their demise.

The Nets had their critics, too.

“I know so many people wanted to see us fail at this juncture, picked us as contenders, and have so much to say at this point,” Irving said after Monday’s season-ending loss, “so I’m just using that as fuel for the summer.”

In Brooklyn, there were problems from the start. Irving refused to be vaccinated against the coronavirus. And because of New York City ordinances that required most individuals to be at least partially vaccinated to enter facilities such as sports arenas, the Nets gave Irving an ultimatum: Get the shot, or stay home. Irving chose to stay home. The season started without him.

By the middle of December, the Nets relented when they allowed Irving to rejoin them as a part-time employee for most road games. In a twist, they needed him, they said, because of the coronavirus itself: Seven of their players had been held out of a game against the Orlando Magic because they had entered the N.B.A.’s Covid-19 health and safety protocols, leaving the team short-handed. The Nets had also lost Joe Harris, one of their top outside shooters, to an ankle injury.

Just weeks into the season, the Nets’ superteam was beginning to come unglued. Younger teams were unfazed by them. It hardly helped that James Harden was scuffling through one of his worst N.B.A. seasons. But he was still taking his share of shots — at Irving. At one point, Harden told reporters that he would vaccinate Irving himself, revealing a glimpse of his frustration. As Harden grew increasingly disgruntled, the Nets pulled the plug, sending him to the Philadelphia 76ers in February in exchange for a package that included Simmons, Seth Curry, Andre Drummond and draft picks.

It was a swift end to the Nets’ superteam experiment, showing how tricky it can be to construct a roster with store-bought stars: You can’t just throw them together and expect it to work, no matter how awesome their individual talent.

Yet amid the wreckage of the Nets’ midseason trade emerged a new superteam — one that was supposed to include Simmons, a three-time All-Star selected No. 1 overall in 2016. The problem was that Simmons arrived with a balky back and self-described mental health issues. He could not practice, much less take the court for games.

The hits kept coming. Durant missed 21 games with a sprained knee. The Nets went on a losing streak, which sent them spiraling down the Eastern Conference standings. The team tried to shore up its backcourt by signing Goran Dragic, but then he tested positive for the virus. New York City eventually lifted its vaccination ordinances, which meant Irving could play in home games. But that left the Nets with little time to build chemistry for the playoffs.

Even then, they had to scramble for a spot in the postseason.

“I wish we had more continuity as a group, but that’s just the league — every team goes through that,” Durant said this week, adding: “It’s a lot of stuff that happens throughout a season that you need to go well in order for you to be a good team, and a lot of things didn’t go our way.”

For the Nets, needing to go through the play-in tournament to get into the playoffs was a minor catastrophe. What happened to the Lakers was worse.

The entire team got vaccinated ahead of the season to avoid the kinds of disruptions the Nets experienced, but other impediments arose. Injuries to James and Anthony Davis, an eight-time All-Star, made continuity difficult. A December coronavirus outbreak meant the available roster constantly changed. Worst of all, the on-court combinations didn’t work.

A lot of that had to do with Russell Westbrook, for whom the Lakers traded last summer, expecting him to be a third superstar alongside James and Davis.

Westbrook, 33, was the most available of the three Lakers stars, but he was also the least effective.

By midseason, it was clear Westbrook was not going to offer the level of superstar play that helped him win the league’s Most Valuable Player Award in 2017 with Oklahoma City. (No M-V-P chants this year.) Opponents began to ridicule his shot selection and air balls. He was uncomfortable with an offense that didn’t run through him. The Lakers had hoped that Westbrook could help stabilize the team when James wasn’t on the court, but that didn’t work.

Westbrook would later accuse Coach Frank Vogel of having a personal problem with him, claiming he’d never before had an issue with any coach or teammate.

“You guys don’t know this, but it was Frank’s and his wife’s anniversary and I actually sent him a bottle of champagne to his hotel room, which you don’t know anything about, because it’s a nice thing to do, nice gesture,” Westbrook said during a news conference after the Lakers’ season ended. He added: “I’m not sure what his issue was with me.”

Vogel was fired after the season, and Westbrook, James and Davis played in only 21 games together. Their union was not productive on the court, and that left the Lakers with limited options for improving the rest of their roster.

On Jan. 9, the Lakers faced a Memphis Grizzlies team on an eight-game winning streak led by the 22-year-old star Ja Morant. Among Morant’s highlights that night were a dunk and a two-handed block. James began to bark at Morant’s teammate, Desmond Bane, 23, who later told reporters he told James nobody was afraid of his footsteps anymore. Their teammate Ziaire Williams played on the same high school team as James’s son, LeBron James Jr., who is known as Bronny.

With losses accruing and nothing changing, tension built.

When James commended other teams’ executives in February, some wondered if those compliments were meant to draw a contrast to Rob Pelinka, the Lakers’ vice president and general manager. James also told The Athletic he hadn’t closed the door on someday returning to the Cleveland Cavaliers.

The next week, Rich Paul, James’s agent and business partner, met with Pelinka and Jeanie Buss, the team’s owner, to assure them that James wanted to be a Laker long term.

The franchise has long valued star players, and it has often won championships. Magic Johnson became a lifelong friend to Buss, after her father bought the team in 1979. Kobe Bryant spent his entire career with the Lakers, winning five championships — three with Shaquille O’Neal and two with Pau Gasol. The team prioritized giving him a noteworthy farewell in his final season over developing the team’s young players.

Other times their affinity for stars has cost them.

During the 2012-13 season, the Lakers added Dwight Howard and Steve Nash, hoping they could chase another championship with Bryant. Injuries and mismatched personalities caused that team to implode. It ended with a first-round playoff loss and Bryant tore his Achilles’ tendon just over a week before the playoffs, which accelerated the end of his career.

The Lakers missed the playoffs for the next six years. They recovered only when James and Davis joined forces and won the 2020 championship.

A first-round exit in 2021 led to the trade with Washington for Westbrook. The Lakers thought that move would help them win the franchise’s 18th championship. It did not.

The Nets had their own title ambitions this season, and were still hoping to coalesce in the playoffs. But the Celtics were waiting for them in the first round, with an arsenal of homegrown stars. They had drafted nearly all of them, including Tatum and Jaylen Brown, their top players, and Marcus Smart, the N.B.A.’s defensive player of the year. Of course, the Celtics had not been opposed to acquiring big-name players in the past: They had traded for Irving in 2017. But after two disappointing and drama-filled seasons in Boston, he bolted for Brooklyn.

And there Irving was on Monday, vowing that Brooklyn was where he wanted to be: “I’m here with Kev,” he said, and they would be “managing this franchise together” with the team’s front office.

They originally came together to win championships, and so far they haven’t come through. But the dreams behind superteams are undefeated — remember, the Lakers and Nets had tried before — even if superteams themselves sometimes fall short.

Irving added, “I’ve been recognized for my greatness, but at this point I really just want to be a part of a great team.”