CLEVELAND — The New York Jets’ remarkable demise on Thursday night wasn’t about Cleveland Browns rookie quarterback Baker Mayfield.

It wasn’t about some grand adjustment the Browns made that the Jets couldn’t handle.

Sure, Mayfield deserves credit for orchestrating a remarkable comeback. And the Browns should be lauded for playing like the Super Bowl was on the line as they notched their first victory since December 2016.

But make no mistake, this ghastly 21-17 loss to the Browns was about the Jets sabotaging themselves. Again.

“We lost our composure,” Jets coach Todd Bowles said. “I told the team that we lost our composure and we should be pissed off up until we play next weekend. That’s the way it’s going to be.”

Here’s the problem: That’s the way it’s been far too often during Bowles’ four seasons coaching the Jets.

They were incensed after they blew a 14-point fourth quarter lead in Miami last season with a slew of mistakes. They were frustrated when the Falcons rallied to beat them in the fourth quarter the next week.

They were furious when they no-showed for the most important game of the season in Tampa the week after that. And they were heartbroken when they blew yet another fourth-quarter lead to the Panthers the next week.

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We could go on because under Bowles there have been way more infuriating losses — the kind where you leave the stadium wondering what just happened — than signature wins

But Thursday night was the worst meltdown. By far.

The Browns hadn’t won a game since December 24, 2016. They had only one win in their last 37 tries. And the Jets were dominating them midway through the second quarter when Isaiah Crowell scored to give them a 14-0 lead.

The Browns had gone 1-72-1 since 2008 when trailing by 14 points at any stage of game (per ESPN Stats & Info) and everyone in the silent building seemed to know it.

And this wasn't' a fluky 14-0 lead. The Jets were dominating. All they needed to do was keep playing hard and smart.

But then the Jets, clearly enjoying another big lead on a national stage a little too much, couldn’t handle prosperity.

The ridiculous butt-wipe celebration penalty by Crowell was the first sign that the Jets’ heads weren’t in the right place. But all seemed well when the Jets’ defense immediately shut down Cleveland for another three-and-out.

And then Trumaine Johnson was called for a taunting penalty. And while the Browns didn’t score everything changed.

The Jets’ defense, which had played three games in 11 days had to stay out on the field for nine more plays and Tyrod Taylor was injured on the final play of the drive, clearing the way for Mayfield to make his pro debut and for a once-quiet stadium to start roaring.

The Jets still had chances to fix it. But they kept making inexcusable mistakes.

Robby Anderson fumbled in enemy territory for the second consecutive week. Morris Claiborne was flagged for a holding penalty on a failed Browns’ two-point conversion. They converted on the re-try, tying the game at 14 and sending the stadium into a frenzy.

And on third-and-5 with less than two minutes left and the Jets trying to drive for the go-ahead score, Brandon Shell committed a false start that helped seal the Jets’ fate.

"We shot ourselves in the foot," receiver Quincy Enunwa said. "And any time you do that it’s always going to be a loss, man. We were doing dumb stuff and just hoping that our athletic ability and play-calling was going to kind of ride it to the end and that’s not the case."

After the game, Bowles insisted the Jets can put this behind them and find success.

“We’re going to have a good football team,” Bowles said. “And we’ll get back to work on Monday and we’ll get ready for Jacksonville.”

And Bowles is right, they have a chance to be a good football team. The Jets have enough talent to put it all together.

But they can’t do it if they’re going to play horrifically undisciplined games like Thursday night. This is Year 4 of the Bowles regime. The Jets are supposed to be past this. If veterans feel comfortable enough to commit mindless, selfish penalties with a big lead, it's easy to see why the discipline isn't there when it truly matters. And you have to start wondering if what Bowles is teaching is working.

If progress doesn't come now, when will it? Why should ownership believe things will be different next year?

After the game, Bowles rightfully shouldered the blame for the loss.

“I’m taking the whole ballgame,” he said. “This whole ballgame falls on me.”

But after yet another gut punch of a loss, and three consecutive years of missing the playoffs, it’s fair to wonder whether Bowles’ methods are working.