Not for nothing was his recent single called “You Can Count on Me.”

Mr. Elgort is a little less precocious than he is innocent, with an openness that is both refreshing and an occasional source of trouble. As a kid, Mr. Elgort — who is 6-foot-4 — used to watch Great Danes frolic with other dogs at the park and he knew he wanted to be like that, gently having fun with everyone. Enthusiasm is his most marked characteristic, and that perhaps makes it hard to imagine people who will envy, rather than root for, his success.

There was the time he tried to explain to Seventeen Magazine that he’d had a nice platonic relationship with his co-star Ms. Woodley, but mangled it by saying, “I’ve never once wanted her sexually.” He delivered a good line to Elle about the virtues of monogamy, saying: “If you like someone and the sex is really good and you enjoy spending time together, why wouldn’t you make that person your girlfriend? Why go around dating random girls and having terrible sex when you can be with someone you really like?” But he didn’t really help himself when, talking about his time at LaGuardia (where he met that girlfriend), he said: “If you’re like me and you love dancers, you just have to walk up to the eighth floor and you can get one.” To which his interviewer, Mickey Rapkin, replied, “You make it sound like adopting a puppy.”

Upstairs at “Good Morning America,” he changed into a Tim Coppens jacket and True Religion jeans, talking about fashion and sounding less like an industry royal’s jaded progeny than a starry-eyed kid who has won the lottery and wants to bro out about it.

“The amount of stuff you get when you’re an actor and you’re in a clothing campaign!” he said, telling of a trip a little while back to Prada, for which he first started doing ad campaigns in 2015. “In the SoHo store, I literally went through and picked anything I wanted off the rack. That was an epic moment! Me and my stylist, John Tan, who’s here, were both, like, cracking up. We were like, are you kidding me? We made it!”

Characteristic of an actor in Hollywood’s current ecosystem, Mr. Elgort said that the vast majority of the money he had made came not from the eight movies he had acted in, but from various ancillary promotional activities. Those include branded Instagram posts, like the one he did in May for the e-luxury site Farfetch, wearing a tiger embroidered Off-White jacket alongside a caption that read: “Made easy may seem far-fetched but it isn’t. Thank you @farfetch for hooking me up w dope threads. In preparation for all this #babydriver press. I found everything I could need.”