One of the things Dwayne Haskins is going to discover about the NFL is that you make or break your reputation in a hurry. That selfie may haunt him. Every time a play goes wrong, the personnel people will make a little mark in their books and wonder if he’s too lax, or casual, or just plain juvenile to run a team. Much as Haskins wants to laugh it off, much as the rest of us might want to cut him a break, it was one of the more embarrassing gaffes by a quarterback in a long time, right up there with a butt fumble. It was the kind of thing that could stick.

A quarterback missed the final snap on the field because he was too busy taking admiring pictures of himself with fans in the stands? When have you heard of such a thing in any league except a bush one? You might say: “Let’s not make too much of this. The NFL is not the most serious endeavor in the world, and the 22-year-old rookie was just overly joyed because the Washington Redskins finally got a victory.” But it does Haskins no favors to soft-pedal this. The fact is, the arbiters of NFL success — the grim, pressure-creased coaches and general managers who determine players’ fates — don’t take kindly to giddy carelessness by quarterbacks.

Haskins needs to listen to the killjoys. He needs to understand why interim coach Bill Callahan wasn’t amused; why Joe Theismann, who has a Super Bowl title to his name, called him “unprofessional” on Twitter; and why Howie Long and Terry Bradshaw murmured “Wow, wow!” — and not in a good way — when they showed it on the postgame highlights. It just wasn’t a good message for an NFL starter. If Haskins doesn’t understand that, he probably needs to spend his Sundays in front of a TV watching cartoons and munching cereal until he grows up.

First of all, exactly what was there to celebrate so exultantly?

It was a skunky, 19-16 victory over the lousy Detroit Lions, who self-destructed with four turnovers behind a second-string quarterback. And if the Redskins hadn’t gotten that Tesla-acceleration kickoff return for a touchdown from Steven Sims Jr., it wouldn’t have been a victory at all. Haskins completed just 44.8 percent of his passes, missed elementary short throws and had only 156 passing yards with no touchdowns against a dreadful defense. It was hardly a performance worth posterizing.

Yet there he was, posing, so unaware of the time on the clock and the circumstances on the field that his helmet was off and his coach couldn’t find him. “We were looking for him,” Callahan said. He didn’t have to look far to find backup Case Keenum, who ran out to take the final snap. Here is a reality that Haskins better understand: A quarterback who is inattentive for even a moment, and who gives up his place on the field to a guy who’s a little readier, tends not to get it back.

Maybe an even bigger red flag than the selfie was Haskins’s performance postgame, trying to laugh it off because he was “so hype,” shrugging, “I’ll get it next time,” and ducking responsibility, claiming that he hadn’t taken any selfies until the game was actually “over.” Then there was the sudden mysterious wrist injury with which he explained his missed throws. These are not the statements of a mature NFL quarterback. They’re the fibs of a kid.

So far everybody has taken it easy on Haskins because he is young and he’s got so much promise and velocity on the ball. But somebody has to say it: Right now, the signs aren’t good with him. His rookie peers, Daniel Jones and Kyler Murray, are on bad teams, too; they’re taking sacks and struggling to make reads and committing young mistakes. But Jones is completing 62.5 percent of his throws for 17 touchdowns to eight interceptions, and Murray is completing 64.6 percent, with 14 touchdowns and just five interceptions.

Haskins, meanwhile, is among the dregs in most vital statistical categories. In three of four games in which he has attempted at least 15 passes, he has completed less than 55 percent of them.

Haskins is fortunate that Callahan is just a placeholder coach. He is fortunate that the Redskins are so starved for any hope that they will tolerate his growing pains. That will probably buy him more leniency than other guys might get. But hopefully someone around him will tell him stiff truths. NFL games don’t turn by much. Players who take plays off are screwing around with people’s livings, their jobs, salaries and bonuses.

Being able to throw one zinger out of every five passes does not make an NFL quarterback. And being airheaded enough to miss the final snap is a suggestion that Haskins doesn’t yet have the habits or the seriousness required, that while he says he wants success, he doesn’t really understand the tedium and work that actually goes into it. Hopefully, he’ll learn those things and a selfie won’t become his defining moment.

For more by Sally Jenkins, visit washingtonpost.com/jenkins.