Over the first nine of his 16 tumultuous months as Ben Simmons’ head coach, Doc Rivers did all he could do to turn on the charm and coax greatness from a lost and fragile soul. No matter how many times Simmons froze up at the free-throw line or gave up the basketball when confronted with the prospect of taking a pull-up jumper, Rivers took care to mute any and all criticism of him.

He accented all the other attributes — the speed and size, the defense, the passing — that made Simmons a still-valuable player, the skills that caused observers, fans, and the 76ers themselves to keep asking an unanswerable question: How good would he be if he would just dare to shoot? It could be a frustrating thing to listen to Rivers heap such praise on Simmons in those postgame media availabilities, not only because it was fair to wonder how deeply Rivers believed what he was saying, but because his comments were a constant reminder of Simmons’ unfulfilled potential.

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Once Rivers hedged in his loyalty to Simmons, though, once he hesitated when asked if the Sixers could win a championship with Simmons as their point guard, the conclusion that arrived Thursday to this strange saga was inevitable. Any shot that Rivers might have had to tap into the talent and production of a fully developed Simmons — of a player who, if his mind were right, could do just about anything on the court — was gone.

Simmons would sooner sit out an entire season than give Rivers that opportunity, and he very nearly did, and now that he’s off to Brooklyn, the spotlight shifts for the Sixers. It shifts to James Harden, to a superstar who has left his two teams in the same kind of chaos that Simmons left the Sixers, and to the coach who gets a second chance to bring the best out of a gifted athlete who can tend to be a handful.

For all the uncertainty and anticipation over when Daryl Morey would say yes to a Harden trade and what such a trade would cost the Sixers, the pressure is off him now … and on to Rivers. Morey didn’t have to sacrifice Tyrese Maxey or Matisse Thybulle, the team’s two most promising young players, to acquire Harden. He sought another star to pair with Joel Embiid, and he got the one he coveted most, the one who, because of both players’ strengths in the pick-and-roll, would seem to complement Embiid perfectly. If the point of “The Process,” initiated back in 2013 by his protege Sam Hinkie, was to build a team with enough top-end talent to compete for and win a championship, then Morey fulfilled his obligations. He did his job.

Now Rivers has to do his. Getting two or more stars to co-exist — to put aside or at least learn to live with each other’s ego and eccentricities — is one of the fiercest challenges for any NBA coach, especially in an era when so many of those stars are willing and able to wield their own power to get their way.

During the 2018-19 season, Brett Brown struggled to quell the conflict that Simmons’ and Jimmy Butler’s clashing personalities and styles of play created. Kevin McHale and Mike D’Antoni ran into similar problems with Harden in Houston, whether the Rockets’ other alpha dog was Dwight Howard, Chris Paul, or Russell Westbrook. And Steve Nash failed so miserably in getting Harden to mesh with Kevin Durant and Kyrie Irving that the Nets became the NBA’s answer to The Bonfire of the Vanities, a big-box-office production so loaded with money and star power that it couldn’t possibly bomb -- except it did.

“Listen, it’s a different day,” Rivers said Thursday afternoon after putting the Sixers through a loose shootaround at their Camden headquarters, “and a lot of it is because they have access to being able to say things. I was a player, and I welcome it. … Overall, and I’m in the minority in this, I think it’s more good than bad. I really do.”

Compared with those scenarios, Rivers had it relatively easy in Boston, where Kevin Garnett, Paul Pierce, and Ray Allen were so hungry and competitive that they generally policed themselves. More, the Celtics didn’t acquire any of those three in a midseason trade, as the Sixers just did with Harden.

The toughest part of such a situation, Rivers said, is “getting it together quickly enough,” but the closest he came to facing the task before him now was in February 2019, when he was coaching the Clippers. They traded their best player at the time — Tobias Harris — to the Sixers, and once they did, no one expected them to be anything more than fodder for Durant, Steph Curry, and the Warriors come springtime. And they were, losing to Golden State in six games in the first round.

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These Sixers are different. These Sixers, with Embiid and now with Harden, have a higher standard to meet.

“It just takes a lot of commitment from the coach,” Rivers said. “But I’ll tell you, it takes a lot of commitment from players when they join new teams because you have to buy in.”

Ben Simmons never did, not while Rivers was his coach, no matter how much Rivers kissed his pass. For the sake of the Sixers’ championship hopes, James Harden has to buy in, and it’s on his new coach now to reach him, to make sure that he does. This is why Doc Rivers is here. Of all the tests during his tenure with the Sixers, this is the one that counts the most.