Jim Montgomery led the Bruins to the best regular season in NHL history in his first season as their coach, but it is seen as a failure because Boston lost in the first round of the playoffs. Winslow Townson/Associated Press

It’s the Golden Age of Boston sports. The past 25 years have seen an unprecedented run of success with our teams.

That type of success creates great expectations from fans, and intense pressure on coaches. Being good isn’t enough when you’re expected to be great.

Sunday night the Celtics were anything but great. Their 128-102 loss to the Heat in Game 3 of the Eastern Conference Finals was an embarrassing letdown that put them on the brink of being swept by a No. 8 seed.

The Celtics, led by a pair of young superstars recently voted as two of the league’s 10 best players, are a far more talented team than Miami. Yet they’re being outplayed and outworked by the Heat, who needed to play two play-in games just to qualify for the tournament.

So what happened, Joe Mazzulla?

“I didn’t have them ready to play, that’s on me,” the first-year Celtics coach told reporters after the loss. “I just didn’t have them ready to play. I just didn’t execute the proper game plan. I didn’t put them in the right mentality to be ready, and it’s my job to make sure that they’re connected and that they’re ready to play, and I didn’t do that.”

Whatever happens in the coming games, it seems obvious that taking the interim tag off Mazzulla was premature. And that his stay in Boston may be short-lived.

It was just under a year ago the Bruins were looking for a coach after firing Bruce Cassidy, who led the Bruins to the playoffs in each of his six seasons in Boston. Jim Montgomery was eventually hired and led the Bruins to the greatest regular season in NHL history.

That team, however, was upset in the first round by the Florida Panthers. Cassidy has coached his Vegas Golden Knights to a 2-0 lead in the Western Conference Final. And Boston fans were calling for the Bruins to make a coaching change again.

There’s much more stability in Foxborough, Massachusetts, where Bill Belichick will be back for his 25th season as head coach of the Patriots this fall. He’s earned that right with six Super Bowl championships on his New England resume.

Still, his future with the organization is a debate that is brought up almost daily on sports radio in Boston. The Patriots haven’t won a playoff game since they beat the Rams in Super Bowl LII in 2019, and have as many losses as wins over the past three seasons.

At Fenway Park, Alex Cora is a manager beloved by most fans, despite the unhappiness many of them have expressed about the state of the Red Sox. Most of that ire has been directed at the way the team has been constructed and the decisions of Chief Baseball Officer Chaim Bloom.

The Sox have gotten off to a surprising start with one of the best offenses in baseball. Cora has used the entire roster and gotten production out of bench players to get the most out of his lineup.

He also benefits from the low expectations surrounding the 2023 Red Sox. Few, if any, fans thought this team would be a playoff contender. If Cora can keep them in the hunt he will get the credit.

For Mazzulla and Montgomery, anything short of a championship will be seen as failure. Cassidy fell victim to the same lofty goals.

In 2023, winning silver or bronze isn’t enough for Boston’s winter teams. That’s the high price you pay to coach in this golden age.

Tom Caron is a studio host for the Red Sox broadcast on NESN. He is a graduate of Lewiston High School.