Before he began his second season as Celtics coach, Joe Mazzulla thought it was important for his team to have an identity. Among the words he used to describe that identity were “mindset” and “toughness.”

Those traits were missing in several moments last season, and came back to haunt them during critical times in the playoffs. The Celtics, too often, let go of the rope. There were several times when they lost their focus. In the Eastern Conference Finals, the Heat were tougher and more disciplined. The Celtics didn’t have a consistent mindset, especially in crunch time.

Through the first several weeks of this season, the Celtics’ mindset seemed to turn a corner. They weren’t underestimating opponents. They responded to adversity well and were the tougher team in crunch time as they kept a level focus.

But that mindset has regressed in recent games. As the C’s embarked on a road trip against inferior opponents, human nature took over. They lost their focus during stretches against the Raptors and Grizzlies, and though they still managed to find victories in those games, they revealed some cracks. Mazzulla wasn’t happy about the win in Memphis and said the Celtics didn’t deserve the victory. A night later, the dam broke in a brutal overtime loss to the Hornets in which they coughed up a nine-point lead with two minutes left in regulation.

The Celtics still boast the best record in the NBA, but this stretch has been their worst of the season as their bad habits have returned, even with a new-look roster. It represents their first real test of adversity as they build the identity that Mazzulla is trying to create.

“I can’t have the expectation of perfection that we’re always going to play well,” Mazzulla told reporters Sunday night in Memphis. “It’s not reality. There are 82 of these things. …

“It’s easy to lump the group of guys that we have coming back as like, they’ve been around, but every team needs to learn different things and go through different stuff, and it’s easy to say you want to be a certain type of team, and then it just gets harder and harder to live that way. And so, the standard is very high for us. The guys in the locker room set a high standard for themselves, and we’re not always going to meet it. So I understand why a game is going to go like this. It’s not going to be the only time, but I don’t have to be happy about it.”

As Mazzulla alluded, it’s a long season and it won’t look perfect every night. It’s easy for a team like the Celtics to lose its edge in November games against inferior opponents. But it’s also an important stretch to learn from as they build good habits that will benefit them in the long run. To their credit, the players seem to understand that.

“We’re talented, and because of that sometimes you can win games just based off of that,” Kristaps Porzingis told reporters in Charlotte. “We don’t want to become that. We want to be a team that shows up and plays the same way no matter who we’re playing against. And that’s still a work in progress, of course.”

NBA admits error

The league’s Last 2-Minute Report on Tuesday confirmed a mistake that cost the Celtics at the end of overtime of their loss to the Hornets.

After Jayson Tatum’s game-tying free throw missed, Miles Bridges corralled the rebound and was fouled by Jrue Holiday with 3.2 seconds remaining. But the clock kept running and the officials did not notice. Instead, the clock stopped with 1.7 seconds remaining.

The Celtics noticed the clock continued to run and tried to get the officials to look at it, but there was no review. The Hornets proceeded to inbound the ball again because they were not in the penalty yet, and Gordon Hayward was then fouled with 0.8 seconds remaining. After Hayward made two free throws to give the Hornets a three-point lead, there was little time for the Celtics to get a good shot. They ultimately did not take a shot as Bridges intercepted the ensuing inbounds pass to clinch Charlotte’s victory.

The league admitted there should have been more time on the clock.

“Although the foul is called with 3.2 seconds remaining on the game clock, the clock continues to run to 01.7 and it is not recognized by the officials,” the league’s report said.

That extra 1.5 seconds would have certainly been valuable for the Celtics as they attempted a game-tying shot on the final play.

“I thought too much time came off the clock, but I guess they couldn’t go back and look at it,” Tatum told reporters. “I don’t know.” …

The Celtics didn’t list anyone on the injury report for Wednesday’s game against the Bucks, which means Derrick White (personal reasons) and Al Horford (rest) are set to return for the marquee matchup.