DALLAS — When you think about it, the task facing the Mavericks isn’t that hard. I mean, when even a 20-year-old knows exactly what they have to do, how tough can it be?

“We just got to make history,” Dallas center Dereck Lively II said.

See? Simple.

Of course, knowing what you need to do and actually doing it are two drastically different things. For proof of this, please refer to Games 1 through 3 of the 2024 NBA Finals.

“Unfortunately, we could just not get over the hump tonight,” Mavericks coach Jason Kidd said after a 106-99 loss to the Boston Celtics in Wednesday’s Game 3 that puts Dallas in the most unenviable position a team can face at this stage of the campaign: an 0-3 deficit in a best-of-seven series.

One hundred and fifty-six teams have been where the Mavs now sit. None of them has climbed all the way out of the hole.

“It's not over till it's over,” said Mavericks MVP finalist Luka Dončić, who scored 27 points with six rebounds and six assists, but who watched crunch time from the bench after fouling out with 4:12 to go in the fourth quarter. “We just got to believe. Like I always say, it's first to four.”

Before you can get to four, though, you’ve got to get to one. And that step’s proven pretty tricky for Dallas.

Kidd’s Mavericks know what they need to do against the Celtics. Prevent them from hunting their most vulnerable defenders to repeatedly collapse Dallas’ perimeter coverage. Keep them from engaging their drive-and-kick game, getting downhill and launching a high volume of open 3-pointers. Fight like hell not to allow them to suffocate the Mavs’ offense by switching ball screens and dragging Dallas into a morass of grinding isolation attacks. Stop them from making timely plays in the clutch.

Through three games, though, they’ve done almost none of the above. It’s the how that continues to elude the Mavs — and that ensures these Finals keep getting played on the Celtics’ terms, in the Celtics’ style … and, ultimately, in the Celtics’ favor.

“You got to give them credit,” said star Dallas guard Kyrie Irving, who broke out of his shooting slump with a game-high 35 points in 45 minutes of work. “Still, we have a belief that we can win one game at a time and take this series a little bit further.”

Given the towering, daunting historical record they’re now confronting — and the team with the historically towering record they’re squaring off against in the process — it’s tough not to think that taking Game 3 represented the Mavericks’ best chance of extending its season. They were back home, in the friendly confines — and, hopefully, friendlier sight lines — of American Airlines Center after their role players had a rough start to the series in Boston. And they were facing the Celtics without game-changing big man Kristaps Porziņģis, whose rare leg injury — officially listed as “left posterior tibialis dislocation” — knocked him out for Game 3, forcing coach Joe Mazzulla to reach deeper into his rotation in search of another option at backup center.

(That option, Xavier Tillman Sr., came up huge, playing tough defense, grabbing boards, blocking two shots and even drilling a corner 3. The Celtics outscored Dallas by nine points in his 11-plus minutes — a massive win on a massive stage.)

This was the Mavericks’ chance, and they knew it, and they came out intent on seizing it. Dallas jumped Boston early, sprinting out to a 22-9 lead behind strong starts by Dončić and Irving, taking turns orchestrating switches onto their preferred defensive matchups — often Jayson Tatum for Luka and Al Horford for Kyrie — and then either getting downhill or rising up for a pull-up jumper.

The advantage would be short-lived, though. As they did in Game 2, the Celtics walked the Mavs down, trusting in both an offensive process that has resulted in more than twice as many catch-and-shoot 3-point looks as Dallas has generated and a defensive strategy that has forced Dončić and Irving to create virtually all of the team’s scoring chances, grinding against tough and physical defenders just to crowbar open enough space to loft up a contested look. The C’s whittled a 13-point deficit down to one by the end of the first quarter and went into intermission with the same deficit despite Dončić and Irving scoring or assisting on 41 of Dallas’ 51 first-half points.

“I thought we were getting really good looks; they just weren't falling,” Mazzulla said. “You just have to stick with it over the course of the entire game.”

And then, in the third quarter, the dam burst:

Boston scored on its first seven possessions of the third quarter, slicing and dicing the Dallas defense to get whatever it wanted, inside and out, and wrest control of the game from the hosts. Jaylen Brown got cooking, shaking off a 2-for-6 first half by scoring or assisting on 23 points in the third — four more than Dallas managed as a team in the frame.

“That was excellent basketball we played to start the third, especially on the offensive end,” said Tatum, who joined Irving in breaking out of the early-series, shot-making doldrums, scoring a team-high 31 points to go with six rebounds and five assists. “I don't know how many possessions in a row that we got a great shot. We made most of them. We might have missed a few. But the way that we started the third quarter was incredible.”

By the time Brown capped his superstar-turn stanza with a thunderbolt of a tomahawk dunk …

… the Celtics held a 15-point lead, and the Mavericks were becoming acquainted with the uncomfortable feeling of back against wall.

“Yeah, you were going to expect a run from them because they had a 19-point quarter,” Mazzulla said. “And just by the type of shots they take alone, you knew they were going to make some kind of run.”

Good call, Joe:

For the second game in a row, the Mavericks fought out of the corner, cutting into a double-digit deficit in the fourth quarter to put themselves in position to win late — “all you can ask for,” as Kidd put it before Game 3. For the second game in a row, though, the comeback came up short.

On Sunday in Boston, it was a 9-0 run that got Dallas within two possessions with 1:15 to go, only to end when Brown and Derrick White converged to snuff out P.J. Washington’s fast-break dunk attempt at the rim. On Wednesday in Dallas, the Mavs ripped off an even more ravenous rampage — a 22-2 fourth-quarter run spanning perhaps the best seven-and-a-half minutes of basketball the Mavs have played in this series, with Dončić dealing, and complementary contributors like Washington and Josh Green finally and blessedly making shots, and their defense helping bog Boston down into the kind of ugly turnovers, curious shots and ponderous, foot-off-the-gas possessions that have at times plagued this historically efficient buzzsaw of a Celtics offense.

But this one, too, would fizzle.

Dončić fouled out, the bill coming due on his lacking defensive effort and some ill-advised earlier physicality. A timely offensive rebound by Brown, followed by Jrue Holiday drawing a costly — and perhaps questionable — illegal screen on Washington in the backcourt (“​​I thought I had my feet set,” Washington said after the game. “But the ref thought otherwise.”), followed by a Holiday baseline drive-and-kick to a waiting Derrick White to cash out from 3, and suddenly Boston was back up six.

But Dallas stayed close, kept grinding, got back within two on an Irving drop-down to Lively with 1:20 to go. The Mavs had their shot. Two of them, in fact: an all-too-rare corner 3 attempt by Washington, and a side-step triple by Irving over Horford on a switch. Both missed. Ballgame — and, if history’s any guide, series and season.

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The Celtics have been the better team from the opening tip. And yet, the last two games have been two-possession affairs in the final minute. Viewed through one lens, that’s cause for optimism for the Mavs — a reason to believe that, if they can just find a way to clean up some of the live-ball turnovers, to tap into some additional wellspring of offensive production, and to mitigate Dončić’s lapses in defensive activity and overall comportment, this series could still turn.

The challenge facing Kidd and his charges? Not falling prey to the glass-half-empty perspective — that they’ve already seen their best chances to make this a series pass them by.

“We're all learning what it means to be on this stage and going through it,” Kidd said after Game 3. “There's a lot of young players on our side who have never done this before. Just understand, we'll talk about that — that this experience that we're going through is a healthy thing. It's not a bad thing.”

It is a bad spot, though — a place you really, really don’t want to be heading into Game 4 on Friday.

Irving said at Tuesday’s practice that failure can be the best teacher. What the Mavericks learned in Games 2 and 3, though, is that at this time of year, the lessons hurt like hell, and they stick with you.

“This is a quick turn, so we don't have time to, like, go to the park or anything,” Kidd said. “We got to figure out how to score the ball, take care of the ball. … We don't have time to go clear our minds. We've got to do better.”