Sometime soon – perhaps during this playoff series, if he has a moment to spare before the Celtics finish off the 76ers, or perhaps once the offseason begins – Brett Brown has to invite Ben Simmons into his office, close the door and sit down for a heart-to-heart talk about the basics of basketball.

Simmons possesses some of the greatest gifts of any Sixers player in any era, speed and vision and a willingness to pass that permeates the entire Sixers team, with so much potential yet untapped. But he is still just 21, far from a perfect player, far from a finished product, and this series against the Celtics and Saturday's 101-98 loss in Game 3 have been loaded with Icarus moments for him, with too many bad decisions born of recklessness and overconfidence.

When Brown pulls him aside for the kind of conversation a coach sometimes must have even with a player as precocious as Simmons, a replay of Game 3 had better already be rolling on the coach's laptop. Simmons had been awful and overwhelmed in Game 2, scoring just one point in 31 minutes, admittedly lost in his own head because he'd finally encountered a coach, Brad Stevens, who had figured out how to build a wall between Simmons and the basket. The numbers suggest that Simmons was better Saturday – 16 points, 8 of 14 from the field, eight rebounds, eight assists – but those solid statistics don't tell the full story of his struggles.

There was an embarrassing missed dunk with just more than five minutes left in regulation and the game tied. It was an uncontested attempt, Simmons as open as he would have been if the Wells Fargo Center were empty, and in his haste and desire to demoralize the Celtics, he didn't take care of his top priority: making sure the ball went through the hoop. There was that inbounds pass in the final seconds of overtime, intended for Joel Embiid and stolen by Al Horford, that lacked the crispness and conscientiousness that every pass in a close, important game must have.

And there was Simmons' most grievous and inexcusable sin of the night: With the Sixers holding a 98-97 lead, with less than 20 seconds left in overtime, Simmons grabbed the rebound of an Embiid miss and immediately flicked the ball toward the rim from the right baseline. The shot clock was off. There was no need, no good reason, to take any shot at all. Yet instead of holding the ball or passing it to a teammate or dribbling for a few seconds or doing anything else that would have burned so much precious time, Simmons disregarded the context of the game, made a mad grab for glory, and back-rimmed that put-back. Worse, when asked about the sequence, he was defiant, insisting that he'd do it again.

"I got a shot that I practice a lot," he said.

You don't regret taking that shot?

"You never know what can happen after that. Had that wide-open shot that I make a lot of the time. … It was natural instinct. I'm right next to the rim. It's a shot I take every practice, every day. Every game, I take one of those. And I missed it. It's happened. That's the game. You miss shots; you make them. You win, or you lose."

Look, one of Simmons' finest qualities – and one of the most surprising, relative to his lackluster season of college ball at Louisiana State – is his competitiveness. He aims to kill all comers, and it can make him a sight to behold when he's at his best. But there's a place for intelligence and prudence, and that shot was wrong in every sense of situational basketball, and Brown knew it.

"If it was a point-blank dunk, you probably would take that," Brown said. "But he didn't do it. It's true: He makes that all the time in practice. There's 19 seconds left. If we had it again, you'd probably bring it back out and let them chase you and foul you and chew up the clock. But on so many levels, this being one of the examples, it's the thing I see and feel the most and sort of internally hear the loudest: that our young guys, at times, look young."

Simmons' mistake wasn't merely a matter of his youth, though. It was also tied to the weaknesses within his skill set. His refusal and/or inability to take and make a shot more than 12 feet from the basket has been an obvious Achilles' heel all season, and it's only now that an opponent – the best defensive team in the NBA, with maybe the best coach in the NBA – has exposed it. And in watching Simmons collect that rebound and hot-potato the ball back toward the rim, it was difficult not to conclude that the last place Simmons wanted to be in that moment was at the free-throw line. He made just 56 percent of his foul shots during the regular season, and his fourth-quarter free-throw percentage was 55.2, his worst in any quarter.

"I would have been confident," he said, which is the sort of thing a young player says even if he wouldn't have been. Yes, Simmons should be a marvel for the Sixers for years to come, but Brett Brown still has to shut that office door tight, look him in the eye, and level with him about his limitations. It's the only way Ben Simmons will ever be the player he can and ought to be.