As the champagne flowed in the Celtics' locker room inside TD Banknorth Garden, Doc Rivers sat alone. The solitude wasn't by design. Rivers had been ebullient on the dais as the 2007-08 Celtics were presented with the Larry O'Brien Trophy after a 39-point championship-clinching win over the Lakers, and had every intention to continue the celebration with the team.

Inside his office -- the sounds of unadulterated joy from the locker room reverberating through the concrete bunker -- he sat in his desk chair in what he expected would be a brief interlude on one of the happiest nights of his life. Then one minute turned into a few as he considered his father, who had passed away during the opening weeks of the season. At one point, Doc's youngest son, Spencer, drenched from a champagne bath courtesy of Kevin Garnett, popped his head into his father's office and pleaded with Rivers to join the party.

"I never got up," Rivers says. "No champagne. No goggles. There was a big celebration in the Legends club. I didn't do any of it."

As the Celtics reveled in the consummation of their magical season, members of Rivers' immediate family, including his mother, Bettye, trickled into his office for a considerably less boisterous celebration. As midnight passed, the Rivers family filed out of the office and made its way to Doc's pad at the Colonnade Apartments, adjacent to Copley Square. Bettye's plan was to cook breakfast for the family soon after the sun rose in less than five hours, but the refrigerator was bare. So just before 1 a.m., Rivers walked across the street to a 24-hour Shaw's and grabbed a grocery cart, roaming the deserted aisles on a Wednesday morning.

"When I go in the checkout line, the clerk comes around from the cash register and says, 'What the hell are you doing in here?'" Rivers says. "I said, 'I'm grocery shopping. We need breakfast.' She said, 'That's true,' then started shaking her head. I didn't see it as strange."

In the days that followed, Rivers enjoyed looking at video shot by his sons of a proud Garnett, every bit as intense in carousal as he was in competition. He had treasured a shared family moment. Yet Rivers has never been able to pinpoint the precise reason he didn't join his team as a celebrant.

"When my kids showed me the video, they said, 'Where were you? Why didn't you come in?'" Rivers says. "I don't even know why. But when I saw it, I thought, 'I'll do it next year.'"

As next year has tumbled into next year, and then the next, the regret of not stepping into that locker room has grown profoundly. Rivers had not only deprived himself of the most rarified, pure jolt of professional happiness sports has to offer but he'd done so on an innocent presumption that championships can be replicated with relative ease if the right talent is assembled -- and the right coach is at the helm.

"When I look back, I'm like, 'What the hell are you thinking?'" Rivers says. "I have a few 'sorries' in my career, but that would be one of them. But it taught me something -- winning is hard."

After his Boston Celtics celebrated the 2008 NBA championship, Doc Rivers retreated to his quiet office in the bowels of TD Banknorth Garden, thinking there would be many such celebrations in the years to come. Nathaniel S. Butler/NBAE/Getty Images

THIS WEEKEND, THE NBA postseason starts without Doc Rivers for the first time in 10 years. He has earned praise for guiding the league's most transitional team through an injury-riddled season that saw the midseason departure of a franchise player, after the offseason departure of another. But whatever pride exists in doing more with less, Rivers has fallen short of his primary objective in Los Angeles.

"When I look back 20 years from now, I will look at our record and know we were really good and really successful," he says. "But it's not what I came here for."

During his five seasons with the Clippers, Rivers has compiled a record of 259-150, but the team never advanced past the conference semifinals. The Clippers are certainly not the first very good squad that plateaued short of a Finals -- all but two teams have been shut out since 2014 -- but there exists something uniquely spectacular about their failure. Stacked with impressive talent playing in its prime, the Clippers were hyped as one of league's best shows, featuring stars with stage presence and title aspirations.

The hire of Rivers was a big splash for the Clippers. Rivers had engineered his exit from Boston -- through furtive back channels that raised eyebrows around the league -- with the advocacy of its two All-Stars, Chris Paul and Blake Griffin. The Clippers even forfeited an unprotected 2015 first-round pick to secure Rivers from Boston and named him their lead basketball operations executive.

To the outside world, Rivers was yet another signal that the franchise was turning the page on its gloomy history -- and making a play for the Los Angeles market and broad relevance in the NBA. Rivers had developed plenty of critics over his career. Those with ties to the Spurs organization, for example, say a strain of disdain for Rivers persists there -- one based on a perception that Rivers actively positioned himself as Gregg Popovich's successor in 1999, when Popovich was rumored to be on the chopping block, and on his aggressive recruitment of Tim Duncan in free agency the next summer (Rivers became the Magic's head coach in 1999).

In some respect, the Clippers presented a high degree of difficulty for Rivers. The first two seasons of the Chris Paul era, before Rivers' arrival, had resulted in 50-plus win seasons, but the team had regressed with a first-round postseason exit in 2013. There was no love lost among the core for Rivers' predecessor, Vinny Del Negro, and the players hadn't exactly forged a mutual affection, either. The team was petulant on the court, and factions were developing in the locker room.

Rivers was hailed as the man who could tame egos and help concoct the chemistry the Clippers lacked. In an SI players poll in 2012, Rivers was selected as the coach players most wanted to play for. In Boston, he had introduced "Ubuntu," an ethic of cooperation popularized by Nelson Mandela, which had become the creed of a temperamental team that had included the Big Three, plus Rajon Rondo, Kendrick Perkins and several outspoken vets. The expectation was that Rivers would do the same in Los Angeles. And for a short while, it looked as if he had.

"In the first year, it was fun," says Jamal Crawford, who played with the team for five seasons. "Then, the [Donald] Sterling thing hit, and he was the best person to lead us through that. 'I'll deal with this, and you focus on basketball.'"

The Clippers might not have been a paragon of unity, and a Game 5 loss to Oklahoma City in the conference semifinals was devastating. But walking across the embers of the Sterling affair during a competitive postseason left the Clippers, on the eve of Steve Ballmer's purchase of the franchise, a more unified team than they'd been a year earlier. Rivers leveraged the goodwill he'd generated by managing the crisis into a hefty new deal that named him the senior basketball operations executive.

But with that consolidation of power came a consolidation of trouble.

Doc Rivers came to L.A with a reputation as a coach who had mastered the art of managing egos. Five years later, his Clippers are an entirely different team, and Rivers has revealed that his coaching acumen was perhaps his biggest strength of all. Andrew D. Bernstein/NBAE via Getty Images

"GUYS WHO HAVE never played for Doc, they all love him for some reason," says Paul Pierce, now an ESPN analyst, who played for Rivers in Boston from 2004 to 2013. "I don't know what it is. I'd never go up to a coach before a game unless I played for him. But these are players who have never played for Doc, and they're always coming over to him, shaking his hand. I was always amazed by how liked he is amongst the league as a players' coach. Because he can be an a--h--- like any other coach."

What is it about Rivers that captivates those players? Pierce -- the only player on all nine of Rivers' rosters in Boston -- points to a range of qualities that constitutes the Rivers mythology. Rivers, as a player, started more than 600 games as a reliable point guard who maximized his talents. Players observed the reverence with which the Big Three in Boston, particularly Garnett, regarded Rivers, who helped cultivate a kind of brotherhood that pro athletes covet. Some grew up listening to his analysis on broadcasts, and admire the talking points from the postgame podium, where he consistently charms the room.

"And he's one of the few black coaches who has won a championship," Pierce adds. "Players recognize that."

Organizational principles can travel in the NBA, but unless you have a Tim Duncan or a Kevin Garnett -- the latter of whom believed deeply in chain of command in Boston and appointed himself the carrier of those principles -- the messages tend to get lost in translation. Such was the case in Los Angeles, where there was also another variable that didn't carry over from the Celtics to the Clippers.

"We had early success [in Boston]," Pierce says. "From day one, we came out winning and won a championship. When you have success, the trust is now there. It's easier because you always have that to lean on. From that point on, it's downhill. 'We did it before, so we can do it again.' Doc didn't have that with the Clippers. They didn't even get to the Western Conference finals, so now people get tired of each other and lose trust in each other. That's what I saw."

Or, as Rivers himself says:, "Once we didn't win, the buy-in got narrower every year."

The "dynamic" with the Clippers, as it was widely deemed, was generally defined as the sum of the interpersonal relationships that dictated the vibe on the team. As time wore on, according to multiple former Clippers players and staffers, Rivers became as prominent a character in the workplace drama as Paul or Griffin or any other member of the roster. And as the authority in charge of managing sensitivities and arbitrating disagreements, Rivers increasingly grew entangled with the rest of the egos.

AFTER PAUL EXITED for Houston, Clippers owner Steve Ballmer reached out to his former point guard. As a relatively new owner, Ballmer wanted to learn from his organization's mistakes and invited Paul to share his thoughts about the current state of the franchise and, more pointedly, his reasons for leaving. When the two met over breakfast, league sources say, Paul stated that Rivers was one of the contributing factors.

More than half a dozen players from the 2013-14 to 2016-17 Clippers declined to speak on the record about Rivers' role in the "dynamic," but a reliable consensus emerged. To a man, they saw a coach who grew frustrated with his inability to manage a complex locker room and who began to act out himself.

Several former Clippers characterized in Rivers a tendency to placate a player by telling him what he wanted to hear, on occasion even criticizing a teammate that player was beefing with. Rivers didn't account for the fact that players, even ones who aren't always simpatico, talk among themselves and exchange notes. Though players regard him as reasonably honest in film sessions and on game night, keeping inventory of what their coach said about specific players became a parlor game among those players and their confidants.