DALLAS — Jayson Tatum remembers how it felt: being just five minutes away from a 3-1 lead in his first NBA Finals … only to watch Stephen Curry, Klay Thompson and Draymond Green lead a 17-3 closing kick to steal Game 4, home-court advantage and, eventually, the championship.

“We learned from our mistakes,” Tatum said Wednesday, two years removed from that lesson, after his Celtics took a 3-0 lead in the 2024 NBA Finals. “We learned from a team at the time that was better than us — that had been there and been over that hump, and mentally tougher at the time.

“We've grown from that. We really have.”

Jaylen Brown remembers how it felt: having crawled out of the insurmountable 0-3 hole to force a Game 7 in the 2023 Eastern Conference finals … only to see Tatum sprain his ankle on the opening possession, all but eliminating his ability to create off the dribble. With the offense suddenly resting on his shoulders and the spotlight trained squarely on him, Brown faltered, shooting 8-for-23 from the field with eight turnovers in a loss he says haunted him for months.

“Last year, just falling short on your home floor, it definitely hurt. It was embarrassing, in my opinion,” Brown said at Celtics practice on Thursday, ahead of Friday’s closeout opportunity in Game 4. “I felt like the team was relying on me. JT got hurt in Game 7 and I dropped the ball. To me, it was embarrassing. It drove me all summer. Drove me crazy.”

It drove him here — to playing like a two-way superstar in the biggest games of his career; to the precipice of hoisting the Larry O’Brien Championship Trophy; to the verge of redemption, or something like it.

“My experiences, the heartbreaks, the losses, have all kind of cultivated into what you see now,” Brown said at Tuesday’s practice. “I don't want to feel that again.”

Which brings us to Luka Dončić — both the unwitting foil in this chapter of Tatum and Brown’s entry in the Celtics’ august history, and the latest young superstar to set out on his own hero’s journey on the Finals stage.

Boston’s brilliant march to Banner 18 is, and should be, the lead story of these 2024 NBA Finals. In some respects, though, it’s the star on the other sideline who stands as the series’ main character … whether he likes it or not.

“For great players, you have to fail to understand how to be successful at the highest stage,” Mavericks head coach Jason Kidd said at practice on Thursday.

On their face, the numbers don’t exactly scream “fail.” Dončić is averaging a series-high 29.7 points, nine rebounds and six assists per game, shooting 56.5% on 2-point tries. Through three games, the Mavericks have been outscored by just four points in the 118 minutes he’s been on the court, and have gotten blitzed by 28 points in the 26 minutes he’s sat.

“My message to him is he's not alone in this,” said co-star Kyrie Irving. “He's played as best as he can despite the circumstances — just injuries and stuff. He's been giving it his all. It's not all on him.”

To whatever extent Dallas has been competitive through the first three games of this series, it has been largely — not solely, but mostly — due to his ability to create and hit tough shots over elite opposition. This, despite playing through a sprained right knee, a sore left ankle and a thoracic contusion that reportedly required a pain-killing injection before Game 2.

And this, despite playing against a Celtics defense that has exposed every weak link in Dallas’ rotation — a lack of shot-making for some players, a dearth of defensive aptitude in others, the inability to create good looks for others virtually across the board. Kidd looked damn near everywhere for answers in Game 3, cycling through 11 different players in the first half in search of “someone to come off the bench and give us a spark,” as he said after the game — and, crucially, in an attempt to ward off “the fatigue [by] trying to get fresh legs.”

Irving is averaging a team-high 41.1 minutes per game in the series, but it’s Dončić — trailing just behind at 39.4 minutes per game — whose legs seem to feel heaviest. He’s scored just eight points on 3-for-15 shooting in fourth quarters in the Finals, and he's routinely looked multiple steps slow on the defensive end in late-game situations, thanks in large part to the Celtics’ persistent efforts to make him work on every single play that he’s on the court.

The defensive game plan implemented by Celtics head coach Joe Mazzulla — switch screens, keep the ball in front, avoid getting into rotation at all costs and force Dallas’ ball-handlers to create one-on-one while also shrinking the floor off of the Mavs’ many shaky shooters to ensure maximum congestion at every opportunity — has forced Dončić, already a usage-rate maximalist, to crank his ball dominance and individual shot creation up to an even higher level against (apologies, Wolves) the highest-level defense in the league, frequently while being dogged the full 94 feet by no less a menace than Jrue Holiday.

And Boston’s offensive game plan might be even more brutal on Dončić.

“When you talk about from the Clippers [series in the first round] to today, his defense has improved,” Kidd said, perhaps charitably, of Dončić. “But when you look at being involved in every pick-and-roll, there's going to be mistakes that take place. That's just the game of basketball. We've just got to limit those mistakes.

“But he is involved in every possession.”

That level of involvement and focus can make for 39.4 very hard minutes per game … and exhausted people sometimes don’t do the best job of keeping their cool.

On Thursday, Kidd mentioned the Mavs needing to play cleaner at the ends of quarters. One such stretch he specifically name-checked: the end of the first in Game 3, when Dallas gave up five points in 30 seconds because Dončić went to the ground looking for foul calls on stepback 3s that missed, was clearly ticked he didn’t get the whistle and was slow to get up and get back into the play, leading to 5-on-4 Boston possessions producing a Sam Hauser 3 and a Tatum dunk.

“Again, just taking one possession at a time,” Kidd said Thursday. “Controlling what you can control: your effort and energy.”

And here’s where we note that the “gotten blitzed by 28 points in the 26 minutes he’s sat” from earlier includes the final 4:12 of Game 3, in which Boston edged Dallas by four points with Dončić watching from the bench after picking up his fifth and sixth fouls in a 26-second span. In a one-possession game. Down 2-0 in the NBA Finals.

That image of Dončić — seated after colliding with Brown, staring at the officials, before throwing his hands in the air and barking at the Dallas bench to “f***ing challenge” the call — is one that will last.

It was a moment born of frustration: at having to repeatedly grind against the phalanx of excellent perimeter defenders that Boston brings to the party every night; at seeing shots he typically finishes at elite clips now clang clear (after shooting 69% inside of 8 feet and 40.1% on stepback 3-pointers during the regular season, he’s down to 58% on the up-close tries and 26% on the stepback triples against Boston); at seeing the passes for the alley-oop dunks and corner 3-pointers that fueled Dallas’ rise up the offensive rankings almost completely eradicated by this Celtics defense.

It was also a moment, though, that laid bare the lack of composure that has plagued Dončić throughout his career, leading to 84 technical fouls over the past five years and his ejection during the fourth quarter of Slovenia’s loss to Canada during the quarterfinals of the 2023 FIBA World Cup.

Part of the superstar’s growth curve is learning how to harness the passion that fuels him and how to channel it in productive ways. That’s a trick Dallas’ favorite magician — now 25, in his sixth NBA season, with nearly 450 combined NBA games under his belt — still hasn’t mastered.

“I just really want to win,” Dončić said at Thursday’s practice. “Sometimes I don't show it the right way, but at the end of the day, I really want to win. I've got to do a better job showing it a different way.”

That’s not an easy thing to do for someone with a predilection toward outbursts. If he’s serious about improving, it’s something he’ll need to meaningfully attempt to address.

“It comes down to just being mature about it,” Mavs center Dereck Lively II, wise beyond his 20 years, said of bickering with the officials. “You're in a very high intensity, very high emotional state in this environment, playing in the Finals. Got a lot of people looking at you, a lot of eyes on you. But all you've got to do is just tune that out. Focus on what you can control. How much energy you put in, how much effort you're going to put in. How much you're talking. How much you care about the situation.”

We know that Dončić has all of the skills to be one of the greatest offensive talents of his generation. How much he cares about the adverse situations in which he puts the Mavericks, though, will go a long way toward determining whether he works to strengthen his weaknesses enough that he can become one of the greatest players of his era.

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“The history is there for us to learn from, when you look at great players and the struggles,” Kidd said Thursday. “You look at [Michael Jordan] and the struggles that he had against Detroit. You look at some of Magic Johnson’s struggles. You look at LeBron [James’] first time around [against the Spurs in the 2007 Finals]. It's there to learn from. But the great ones, they use that going into the next season, or the next couple of seasons, to try to get back there. Because now they understand experience is a big thing.”

That growth won’t happen for Dončić overnight. But the Mavericks’ fate — of extending this series, and of being able to one day get over the hump — will hinge on it happening. And the sooner, the better.

“You've got to go through lows first to go on top,” Dončić said. “I think that's great experience … I'm 25. I've got a lot of things to learn. This is my first NBA Finals, so I'm going to learn from it, for sure. But we're not in the offseason yet. They've still got to win one more game.”

And in Friday’s Game 4, Tatum, Brown and the rest of these rampaging Celtics will look to finish their story by teaching Dončić one more lesson that might help him kickstart his over the summer.

“In moments of embarrassment, in moments of coming up short, falling short is where the most growth takes place,” Brown said.

Come Friday, then, Luka wins, or he learns. Class dismissed.