As Sam Darnold thought back to his up-and-down rookie season, he pinpointed his biggest mistake.

It wasn’t lack of accuracy, which in part led to 15 interceptions and a pedestrian .577 completion percentage, or any specific routes he struggled hitting consistently. It wasn’t underestimating the speed of the game or the heightened skill level of the NFL compared to college.

It wasn’t physical at all, in fact.

“I think looking back on it,” the Jets’ second-year quarterback said Monday, “I would’ve communicated a lot more.”

Darnold didn’t ask for help nearly enough, he now believes. He was busy trying to get his feet under him, doing his best to adjust to the new league. While he had mentors such as Josh McCown and Teddy Bridgewater to learn from, veterans he beat out for the starting job, he too often put the onus on himself.

A year later, the former third overall pick in the draft — the face of the franchise some believe is the organization’s first true franchise quarterback since Joe Namath — isn’t making the same mistake.

“I think for me it’s just being real with what’s going on,” he said. “Communicating is key, especially going through a new offense.”

Darnold makes sure to share his ideas with new coach Adam Gase and offensive coordinator Dowell Loggains. On the sideline, he’ll bounce thoughts off his new running back, Le’Veon Bell. If he has a question, he doesn’t hold back. There are plays he never ran before in Gase’s system. Some of it is completely new.

“So, if I don’t run it right or if I don’t like it the first time around, I can’t give up on the play. I’m going to take coach’s word for it, and really just continue to grind through it,” he said. “There are going to be some growing pains with some of the plays, but I’m loving the playbook so far. The plays are in there for a reason — because they work. As long as I keep going with them, and understand that they’re good versus certain coverages, then I’ll be OK.”

When a play doesn’t go well, Gase will ask him, “Are you not feeling this?”

Darnold’s response is often the same.

“No, just keep calling it,” he will say.

He’s already impressed Gase. Darnold will be given freedom to audible at the line of scrimmage during the regular season.

“Oh yeah, that’s where it gets real fun,” Gase said with a smirk. “We’ll make sure we notate which ones he changes.”

Darnold’s maturation process might be the most important aspect of this Jets season. He seemed to hit his stride late last season, throwing just one interception and tossing six touchdown passes in his last four games after missing time with a sprained foot. The Jets can only hope that finish has a carryover effect.

“Some of the throws he makes are ridiculous,” Gase said on ESPN Radio later Monday. “When everybody’s collapsing on him, he’s square, shoulders parallel, and he flicks it 50 yards. I’m like, ‘What is that?’ … His arm looks phenomenal right now.”

So far, the signs are basically all positive, coaches and teammates say. Their quarterback seems more sure of himself — which should only help once the games begin — knowing he belongs.

“I definitely think there’s a more comfortability I guess you can say with my teammates, communicating with the coaches. Even here talking to the press, I feel more comfortable,” Darnold said. “After doing it for a year, I grew a lot after last year and going through that. I feel like I’m definitely a lot more comfortable.”