Forsberg: Celtics left to ponder what could have been originally appeared on NBC Sports Boston

BOSTON -- No matter how it arrives, the end of an NBA season always feels abrupt. It’s like you’re sprinting on a treadmill and someone kicks out the plug. Next thing you know, you’re hanging upside down from the electronic display wondering what just happened.

The Boston Celtics’ 2021-22 season, which featured an improbable and unprecedented midseason turnaround, along with an exhilarating run to the NBA Finals, ended Thursday night with a Game 6 loss to the Golden State Warriors at TD Garden.

This one is going to sting. The Celtics navigated a playoff gauntlet but there was an unexpected opportunity for more. The Warriors were overflowing with playoff experience but were far from unbeatable.

The Celtics too often beat themselves, though the Warriors certainly did their part over the final two games. Boston could not get out of its own way. The Celtics turned the ball over in batches, their offense fell into the bad isolation habits that defined the ugly first half of the season, and this team couldn’t muster any of the resiliency in the Finals that had previously been their postseason calling card.

Boston is left to ponder what could have been. A fast start inside a raucous Garden delivered daydreams of a Game 7 showdown in San Francisco. Steph Curry and his sharpshooting pals burst that bubble with a 21-0 run stretching into the second quarter. And no amount of Ime Udoka timeouts could steady Boston, which tried feverishly to rally close in the second half.

The Celtics were five minutes away from a 3-1 series lead just six days ago. Then everything went to hell. Boston’s offense sputtered at the finish line of Game 4 then improbably stalled out again at the start of Game 5. The Celtics projected confidence in the ramp up to Game 6 but came unglued just long enough for the Warriors to build a big cushion on Thursday night.

Even in a city where the only desirable outcome is a championship banner, it would be too harsh to suggest the season is a failure because of the Finals outcome.

It is, however, fair to lament a missed opportunity, no matter how farfetched even reaching this stage might have seemed four months ago.

The Celtics were 18-21 after an impossibly bad, national TV loss to the Knicks in early January. After that game, Boston sat in 11th place in the East and showed few signs of the team they would soon become.

Boston went 33-10 over the final 43 games of the season, posting the NBA’s best offensive and defensive ratings over a dominant three months of play. First-year coach Ime Udoka scoffed at the notion that his team ought to dodge the Brooklyn Nets in Round 1 of the playoffs. He implored his team to chase the No. 2 seed and was rewarded with a first-round sweep of Kevin Durant and old friend Kyrie Irving.

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A path to the NBA Finals soon emerged, particularly with Bucks All-Star (and Celtics shredder) Khris Middleton sidelined for the conference semifinals. Still, the Bucks won two of the first three games in Boston, including what should have been a demoralizing Game 5 triumph inside TD Garden. Unfazed, the Celtics watched Jayson Tatum outduel Giannis Antetokounmpo in Game 6 in Milwaukee, then rode unlikely hero Grant Williams to a Game 7 triumph.

Boston had to grind again in the East finals. This time it was Jimmy Butler producing an otherworldly Game 6 effort in Boston to extend an already ultra-physical series. The Celtics calmly flew to Miami and won on the road to punch their ticket to the Finals.

The title round will leave a sour taste in an otherwise sugar sweet season. Udoka pushed his young team hard early in the year but was rewarded with monster growth over the final months. President of basketball operations Brad Stevens rolled the dice a couple times during his first year at the helm (particularly with acquiring Al Horford and Derrick White) but constructed a roster in which all the pieces complemented each other and pulled in the same direction.

Jayson Tatum made multiple leaps en route to an All-NBA first team nod (and a sixth-place finish in MVP voting). Tatum’s Finals struggles will cause some to re-litigate his status in the NBA hierarchy but the progress he made, particularly as a playmaker, was undeniable. The Celtics are well-positioned with this 24-year-old at the helm deep into the future. He will have no shortage of motivation given the way his season ended.

Jaylen Brown is still not a finished product. Robert Williams might be the key to Boston’s championship hopes with the way he impacts the team on the defensive end. Marcus Smart proved he can quarterback a top-tier offense when installed as the primary point guard and won Defensive Player of the Year along the way, too.

The Celtics cannot bank solely on internal development to ensure another trek to the championship stage. Stevens will have avenues to improve the team this offseason and, if ownership is willing to splurge on a contender, the Celtics can further beef up a roster that was a little thin on depth.

The offseason will be short because of Boston’s deep trek but there will be plenty of time to ponder how the Celtics can reload.

For now, it feels important to savor the improbability of what just unfolded. All that was missing from this storybook season was the ending. Maybe the final scene will motivate a young core to ensure these sort of opportunities don’t slip away again.

That the Celtics would be playing basketball in mid-June seemed utterly laughable just a few months ago. Many cackled when FiveThirtyEight projected a possible Celtics-Warriors Finals matchup in March, and then it came to fruition.

It’ll take a while to get past the sting that lingers. There’s a pit in the stomach of Celtics fans because the team hindered its own quest for an 18th title.

Eventually, this run will be romanticized. Along the way, it felt a little bit like the Isaiah Thomas-led surge of 2017. But that team outkicked its coverage; this one actually had the talent to get to the finish line of a championship season. It just wasn’t ready for the moment.

Maybe there will be other opportunities, though they are never guaranteed. If the Celtics win a title down the road, maybe this season will be even more fondly remembered. Maybe it’s just one of the first chapters in a string of novels about the core pieces of this team.

But for now, it ends on a cliffhanger. Like your favorite Netflix series, there’s a long way until the next season drops. It’s going to be a brutal wait to get this treadmill plugged in again and ramp the bike back to full speed.