By Matthew Geagan, CBS Boston

BOSTON (CBS) — The shock has passed and now reality is setting in. And boy did the Celtics blow a great opportunity down in the NBA bubble.

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While thoughts of “the future is bright” and “they’ll be back next year” can briefly improve your mood, the bottom line is that the Celtics had a golden opportunity to get over the hump and finally make the NBA Finals, and they flat-out blew it. They held fourth quarter leads in all six games of the Eastern Conference Finals against the Miami Heat, and they ended up losing four of those contests. That isn’t acceptable, not from a team that tried to tell us all season long that they were title contenders.

Heads aren’t going to roll, because that isn’t the Celtics’ style. And really, they should be back next season, and you hope that this sting and disappointment of coming up short once again will provide plenty of motivation next time around. There are no more built-in excuses for the Celtics like the last two times they lost in the Conference Finals; they didn’t lose to LeBron James and they can’t point to a rash of injuries for coming up short. And this season doesn’t have a Kyrie blanket to drape over the smell of defeat.

The blame doesn’t fall on any one player or person. This one sticks to just about everyone up and down the roster and one the sideline. So let’s play the blame game and figure out why the Celtics came up so short against the Miami Heat, squandering the team’s best chance to compete for an NBA title during the Brad Stevens era.

Brad Stevens

Celtics head coach Brad Stevens. (Photo by Kevin C. Cox/Getty Images)

Stevens is a great coach, but he had his issues this postseason, especially against the Heat. Even the most hard-wired Brad Bots would admit that he got outcoached by Erik Spolestra, who is now heading to his fifth NBA Finals.

His big man rotations were a mess. He’d turn to either Robert Williams or Enes Kanter for quick spurts in the first half, and even if they had success, they’d stay on the bench in the second half. Williams was instant energy off the bench, and even if he still bites on every single upfake, he still could have helped at times in the second half. Kanter’s minutes being limited made sense, since the offense he provided was usually negated by his lack of defense, but even he could have helped for additional short bursts in second halves.

Losing Gordon Hayward from the starting five, which led to losing Marcus Smart off the bench, hurt the continuity of the Boston bench. It caused Stevens to mix and match throughout the playoffs, and even when Hayward returned, Stevens had to slowly work him back. He really only had Brad Wanamaker and Grant Williams as steady(ish) bench contributors. Both played admirably, especially Williams in his brief stints, but again, Stevens would only rely on them for short minutes. This may fall more on Danny Ainge for his inability to build a decent bench, but Stevens is the guy who has to make it all work. He did not do that in the playoffs.

And then there were the blown leads, which Stevens could do little to stop. Boston won just two fourth quarters against the Heat, who averaged 31 points in the frame. That’s where his rotations and timeouts came into play, and Stevens was lacking on both fronts.

The coach is always the first to admit that he needs to be better, and he has a few more things to focus on over the offseason.

Marcus Smart

Celtics guard Marcus Smart. (Photo by Douglas P. DeFelice/Getty Images)

Marcus, I love you. As long as I still hold the respect of my two young sons, they will be taught to never slander Marcus Smart in our household. But, Marcus, my man, you took too many shots against the Heat.

Smart has always been one of those “No. NO! NOOO!!! YES!!!!!” kind of shooters, but he will occasionally believe he’s both Steph Curry and Klay Thompson — or even better than those two sharpshooters. Sometimes, Smart hitting his first few shots from downtown does more harm than good.

He took 22 shots in Game 6 — second on the team to Tatum’s 26 attempts. Of those 22, 13 of them came from three-point range. Only four went in. His six shots during the fourth quarter matched Tatum and Jaylen Brown’s shot total. The Celtics probably would have been better off with either Tatum, Brown or Kemba Walker (seven shots in the fourth) taking a few of those looks.

Overall, Smart averaged 14 shots per game against the Heat, eight of which were from deep. He hit 39 percent from the floor and just 27 percent from three. Marcus, please, we’re begging you — go to the basket more.

We all know of the impact that Smart makes away from the ball and on the defensive end, but he is prone to fall in love with his shot. When those shots aren’t falling, they are rally killers for Boston, and that really hurt the Celtics at some really important moments against Miami.

Tatum’s Slow Starts

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Jayson Tatum. (Photo by Kevin C. Cox/Getty Images)

Jayson Tatum is a star and a great building block for the Celtics. He is oh so close to being considered a superstar. But he’s not there yet.

Even superstars are susceptible to scoring slumps, but Tatum’s cold starts to Games 4 and 6 did Boston no favors as they looked to claw their way back into the series. Before erupting for 28 points in Game 4, Tatum suffered through a scoreless first half, going 0-for-6 overall and 0-for-4 from three. The Celtics were only down six at halftime, but in a three-point loss, one more Tatum make could have made the difference.

He didn’t go scoreless in the first half of Game 6, but Tatum started the game 0-for-7. His passing was still crisp with five assists before he made his first shot, but the Celtics aren’t going to win many games when it takes Tatum halfway through the second quarter to see the ball go through the hoop.

This could also fall on Stevens, who should have drawn up a few plays to get Tatum an easy bucket or two as he was pressing from deep. Remember when Stevens used to draw up successful ATO plays? Those were the days…

Kemba’s Defense

Kemba Walker tries to defend Jimmy Butler during the Eastern Conference Finals. (Photo by Douglas P. DeFelice/Getty Images)

Kemba Walker was a breath of fresh air for the Celtics throughout the season, from all those big shots he hit to that infectious glowing smile. His leadership made the Celtics fun to watch again.

But like Boston’s previous leaders at the point — Isaiah Thomas, Kyrie Irving and the guest appearance of Terry Rozier — Walker is limited on the defensive end. And that hurt Boston’s all-around team defense at times.

Hayward’s Health

Gordon Hayward (Photo by Kevin C. Cox/Getty Images)

Hayward gave the Celtics a nice boost in his Game 3 return, and it was admirable that he chose to stay with the team instead of leaving the bubble for the birth of his son. But it’s very clear that the Celtics cannot rely on Hayward to be healthy when it matters most.

Reports say he was only 65 percent when he hit the floor in the East Finals. He had no lift on his jumper and was timid to take shots. Even with his stellar passing, having no shot was detrimental to the flow of the offense.

Hayward has one more season — at $32 million — to live up to his max contract in Boston. Good luck with that.

Where Was The Bench Help?

Celtics President of Basketball Operations Danny Ainge. (Photo by Tim Bradbury/Getty Images)

Danny Ainge loves his draft picks. Probably too much. It’s even more infuriating when he decides to turn those picks into more future picks instead of something that would help the current Celtics team.

We know that he loved Tyler Herro at last year’s draft, but he didn’t do anything to move up to make sure Pat Riley didn’t steal away the Kentucky sharp-shooter. That’s the easiest second guess because we just watched Herro torch the Celtics, but it’s pretty valid.

But Ainge did nothing at the trade deadline to help the team either, which hurts even more after watching Jae Crowder and Andre Iguodala do damage against Boston. All Stevens had to work with off the pine was the revolving door of Williams and Kanter, rookie Grant Williams and Brad Wanamaker, all of whom have their limits.

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The Celtics sorely needed a scorer off the bench, and Ainge never really provided them with one. That has to be one of Ainge’s many focuses this offseason.