BOSTON – One moment can change everything. No one knows that better than Jabari Bird.

His moment arrived on Oct. 20, 2017, and as he tells it, that moment set him up for the seminal achievement of his 24-year-old life: signing his first guaranteed contract in the NBA.

Bird’s story begins three nights prior, on Oct. 17, when he was at his family’s home in the Bay Area, casually enjoying a basketball night on television. He was on the couch watching the Boston Celtics – the team with which he had recently signed a two-way contract – open up the NBA season with a showdown against LeBron James and the Cleveland Cavaliers.

Bird was watching that game on the television rather than from the bench because he was a distant thought when it came to Boston’s Opening Night roster. The Celtics didn’t require his services, and as such, he was set to open up his season with the G-League’s Maine Red Claws the following week.

That plan changed – and in a hurry – on Opening Night.

Gordon Hayward went down early in the contest with a devastating ankle injury, joining Marcus Morris on the list of injured Celtics. All of a sudden, Boston was down to 12 available players, and it needed that guy on the couch in Northwest California.

Bird joined the team the next day for its home opener but did not play as the C’s fell to 0-2 on the season. He also didn’t play during the first half of Boston’s Oct. 20 game in Philadelphia.

He was, in essence as the last player on the bench, an insurance policy for additional injuries or foul trouble.

But with 6:07 remaining in the third quarter of that game against the Sixers, and with Boston trailing by eight, his moment arrived.

Brad Stevens, seeking a defensive spark, glanced down the sideline and uttered three syllables that changed everything for the rookie: “Jabari!”

“For coach to look down to the end of the bench and to trust me to go in and to guard one of the better perimeter shooters in the game (J.J. Redick),” Bird recently told Celtics.com, “that did a lot for my confidence for him to even consider putting me out there.”

And when he did get out there, he made it count.

Redick, who lit the Celtics up for 15 points during the first 27 minutes of the game, scored only four more points during the final 18-plus minutes following Bird’s entrance into the game. Bird played nearly 14 of those minutes, and the Celtics outscored Philadelphia by 12 points during that time frame as they tallied their first win of the season.

Just like that, Bird began to take flight.

He would soon go on to build a successful campaign in Maine, where he averaged 19.3 points, 5.7 rebounds, 2.7 assists and 1.4 steals per game. Then he opened the league’s eyes during July’s Summer League in Las Vegas, where he led Boston in scoring with an average of 16.8 PPG.

As a restricted free agent this offseason, he wasn’t sure what was going to happen, but a handful of teams contacted his agent about the potential of signing Bird to a guaranteed deal. Boston would soon offer a deal of its own, and on July 26, Bird signed his name on the dotted line.

In a year’s time, Bird went from nearly going undrafted as the 56th overall pick in the 2017 NBA Draft, to fighting through a two-way contract, to earning a contract with the Celtics. He credited his progress to that single moment on Oct. 20, when Stevens called his name.

“I think that’s what catapulted me forward to having the year that I had last year,” he stated matter-of-factly.

Bird went on to elaborate on why that moment is so important to him.

“Getting drafted is one thing. That’s an honor. Playing Summer League and having some good games, that’s one thing,” he said. “But when you do it in an NBA game, regular season, road game, hostile environment, like… it just felt like I really belong at this level. Moving forward, I just knew: I’m here for a reason.”

The Celtics agreed, and that's why Bird is now here to stay. Still, challenges lie ahead.

Bird, who was recently told by teammate Aron Baynes that he's still a rookie, understands that he’s looking up at a loaded roster, particularly at his position. He plans to use the lessons he learned by observing one of his friends last season to navigate such circumstances.

“One guy that I watched a lot last year was Semi (Ojeleye),” Bird said of his teammate. “There were moments when he played 25, 30 minutes and had a really good game, and then next game not play. So I was just watching how he carried himself.”

Ojeleye enacted the mindset that Stevens preaches: never get too high, never get too low. It worked for Ojeleye, and now Bird wants it to work for himself.

“I want to have the same mentality,” he said. “Just come in every day, not knowing what’s going to happen, and just be ready to go.”

Ironically, that’s exactly what happened back in mid-October, which taught Bird a memorable life lesson: Seize the moment, and that moment can change everything.