When Jayson Tatum got in trouble in elementary school, it was often Kobe Bryant’s fault. Teachers weren’t thrilled when the Celtics breakout star would sit in class and watch YouTube highlights of the Mamba. “The older I got, the more they understood that I was going to be in the NBA,” Tatum tells me, grinning. “I mean, school was very important. But I needed to watch basketball.” This often caused trouble at home, too, when he’d try to re-create his favorite move: Kobe’s impossible-to-stop baseline fadeaway.

“I remember my dad used to hate that I did it,” says Tatum, tucked away under the foliage in the back of L.A.’s Sunset Marquis. “It was such a bad shot for a second grader.”

All the more surreal, then, that he says this in L.A., the day after the Lakers legend generously decided to mentor the young Celtic, a rare one-on-one workout between longtime East-West rivals. And what was Professor Vino’s advice for his new student?

“Shoot every time,” he recalls. “Pass if you have to. But if not, shoot it.”

Suit, $2,500, by Prada / Shirt, $442, by Wacko Maria at Union Los Angeles / Earrings throughout, his own Coat, $1,495, by Boss / Sweatshirt, $595, by Fear of God / Shorts, $450, by Just Don / Sneakers, $110, by Nike / Socks, $8, by American Apparel

If Tatum plays the way he did to cap his first season in the league—putting on one of the greatest rookie campaigns in playoffs history and leading the Celtics to within minutes of an Eastern Conference title—that “me first” (and second, and third) Mamba mentality just might turn him into the NBA’s next great killer. After all, he’s armed with a Kobe-like arsenal of skills: a deadly jumper, balletic footwork, a see-you-later first step. Even on a team with Kyrie Irving, Tatum has emerged as the bedrock of Boston’s future. See: Game 7 of the Eastern Conference finals, where he put LeBron James on a poster.

Not bad for a guy who less than seven years ago was a gangly teenager (in, it’s worth noting, a Kobe Bryant jersey) thirstily tweeting at LeBron James for a follow-back. (James did eventually follow him back.) James also welcomed Tatum to the league by swatting his first-ever NBA shot, a rookie debut during which, Tatum says, he was “extremely nervous” and more than a bit starstruck. “Early in the season, when we played LeBron or the Greek Freak or Golden State, right before tip-off, I would just look at them,” he says. “Like: This is my life. Damn. I’m 19, right next to KD, getting ready to play basketball.”

Now he’s 20—and dunking on them.

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“I think that anytime a guy has a year like that as a rookie, if you say that you expected it, I don’t know that that would be honest,” says Celtics coach Brad Stevens. “He didn’t ride the emotional roller coaster like a lot of young players do. And that kind of goes back to who he is. He’s got a maturity about him that is unlike most people his age.”