After this crushing setback, what does the future hold for the Celtics?

Robert Williams (left) scored 10 points and Grant Williams had 3 in Game 6 of the NBA Finals.Jim Davis/Globe Staff

There will be a scar.

That much we know, with the wound of the Celtics’ loss to the Golden State Warriors in six games still fresh.

Only in the coming seasons will we learn whether it’s the kind of scar that doubles as a badge of pride, a reminder of a hard but necessary lesson on the journey to ultimate success.

Or perhaps it will be the other kind of scar, a jagged and permanent what-if, a reminder of a moment gone wrong, never to be righted or avenged.

The Celtics’ exhilarating, exhausting season ended Thursday night with a 103-90 loss to the Warriors, now four-time champions in the Steph Curry era.

The Warriors, who won the last three games of the series, are as worthy as a champion can be. There is no shame in falling to Curry, Klay Thompson, and yes, even loudmouth-who-backs-it-up Draymond Green. They are legends of their time, and of all time.

It was fitting that the final defeat served as a microcosm of the Celtics’ worst and best characteristics, and doesn’t it always seem to go that way?

They were careless with the basketball when they had it (22 turnovers, dropping them to 0-8 in the playoffs when they committed at least 16), and failed to secure it too often when they needed it (the Warriors collected 15 offensive rebounds).

They did manage 27 assists, but the usual fits of my-turn-your-turn isolation ball that stagnated the offense had to be endured too. Jaylen Brown scored a bunch (34 points) but made no one around him better, while Jayson Tatum (13 points) lost his bearings at the worst time, which would be concerning if it weren’t a rite of passage for so many NBA superstars.

I do think it’s fair to say the Celtics, even with their magnificent turnaround after an 18-21 start, never fully repaired their offensive flaws. They just made them go away for a while.

Yet they never quit, not after watching an early 14-2 lead in Game 6 evaporate as the Warriors tore off a 21-0 run bridging the first and second quarters … or when that ballooned into a 54-39 lead at halftime … and not even when the admirable, annoying Curry stuck a long three to put the Warriors up, 72-50, with a little over six minutes left in the third quarter. (I will admit this is when I thought it was over. Admit it. You did too.)

The Celtics’ defensive effort never waned, and with 44.1 seconds left in the third quarter, a conventional 3-point play by 36-year-old Al Horford (19 points, 14 rebounds, 4 3-pointers, 1 block, 1 flex after the block) cut the Warriors lead to 9 (74-65), the first time it had been single digits since midway through the second quarter.

The Warriors, too often aided by a Celtic mistake, always had an answer, and after one last gasp of a comeback attempt was stifled in the fourth quarter, coach Ime Udoka removed his starters with 1:03 left and his team down 13. It was time, because they were out of time, but it was tough to see them go.

If the end left you aching, it’s because we know that these are the losses that linger. Every time I see Kendrick Perkins on ESPN or NBC Sports Boston — every single time — I think of the knee injury that kept him out of the Game 7 loss to the Lakers in 2010. Hey, and did you see that Rasheed Wallace got a coaching job on Darvin Ham’s Lakers staff? If only he’d been in better shape in that Game 7 …

The Celtics’ appearance in the Finals this year was their first since the loss in ‘10, and how long it lingers — and how noticeable that new scar will become — depends upon what comes next. In the long view, the Celtics are in excellent shape.

Tatum and Brown have proven they can be the top scorers in tandem on a contending team and are entering their prime. The team’s core is signed. Robert Williams, presuming his knee is healthy, is still ascending, and Horford still insists on playing like he’s five years younger than he is.

Udoka is the ideal modern coach to lead them. Goodness, how right did they get that hire? I’m almost annoyed that he never got an opportunity before this.

But there must be alterations. Derrick White, Grant Williams, and Payton Pritchard — the three core bench players — were downright dismal late in this series. White’s brilliant Game 1, when he hit five 3-pointers, feels like it happened in a different time and place. The three of them were a combined 2 of 10 from the field and minus-64 in Game 6.

A veteran shooter or wing to lengthen the bench by one more reliable option is necessary. Am I alone in believing that Aaron Nesmith will emerge as a useful contributor once the game slows down for him? I’m not sure he’s the shooter he was touted to be, but he defends as if his shoelaces were on fire.

It’s easy to overlook now, but this team did validate itself along the way. The Celtics swept the loathsome Nets, dethroned Giannis Antetokounmpo and the champion Bucks by coming back from a 3-2 deficit, and won a Game 7 in Miami. So many satisfying memories will come to the forefront in the weeks ahead.

Unfortunately, at this moment, all we can think about is how it ended, and how close the Celtics were to fulfilling a championship dream. We haven’t had a reminder of this for a dozen years, but it turns out it remains true: The deeper into the postseason you go, the more the ending hurts.

And the scar that comes as a result? It never fades. But it’s up to these Celtics — these talented, maddening, dedicated, annoying, resilient Celtics — whether it’s ultimately a reminder of a lesson learned on the way to greatness, or a singular opportunity lost, never to be presented again.

I believe it’s the former. Just wish we didn’t have to find out this way.