BOSTON – “I shouldn’t even be in the NBA.’’

So would Avery Bradley say to himself.

“I remember I was at home in my bed, like, I’m not an NBA player,’’ he says. “I wasn’t playing and my family would be like, ‘Why aren’t you in the gym?’ They don’t know I was in the gym for hours every single night. I’m working so hard and nothing is paying off.’’

How many rookies believe themselves to be better than they really are? Bradley, an undersized shooting guard, arrived to the Boston Celtics six years ago with the opposing, self-disparaging point of view. He was certain that his own doubts were shared by everyone around him, including coach Doc Rivers and his assistant at the time, Tyronn Lue, who has since become head coach of the champion Cleveland Cavaliers.

“I’m pretty sure they didn’t think I would be who I am today,’’ Bradley says. “Not pretty sure. I know they didn’t. I know.’’

Did current coach Brad Stevens see Bradley’s potential?

“No,’’ answers Bradley.

What about Danny Ainge, the Celtics GM who picked Bradley No. 19 in the 2010 NBA Draft? Didn’t he see what Bradley could become?

“Danny too,’’ says Bradley negatively. “He might say he did. But I think I shocked everybody on a daily basis.’’

The context is important. If only you could see Bradley’s quiet demeanor, hear the understanding in his voice, as he makes these claims. He is neither surly nor angry. On the contrary, he empathizes with his supposed doubters. He understands why they didn’t see the future in him.

“I still think it’s hard for people to believe it,’’ he says of the talents that are emerging now, at age 26, in ways that cannot be ignored. “Because I am so quiet, you don’t really know what I’m thinking. You don’t know if I’m working hard on my game, you really don’t know.’’

This is from Avery Bradley, arguably the best backcourt defender in basketball. At 6-foot-2, he is leading Boston in rebounding (7.3 per game) while playing all-out at both ends. He is the Celtics’ No. 2 scorer with 17.9 points, their leading 3-point shooter at 41.8% on 5.1 attempts per game, and he has transformed himself into a reliable playmaker. He is an All-Star in the making.

“I don’t think they saw it,’’ insists Bradley without bitterness. “I don’t think a lot of people saw it.’’

He is understanding of the negative point of view because he has been its leading proponent. As much as Bradley has sought to win over Rivers and others, the hardest person to convince of his potential has been himself.

Most painful call

“I was driving home from New York,’’ Bradley says. “It was probably the worst call I ever got.’’

It came from one of his brothers, with whom Bradley had been feuding.

“I wasn’t talking to my brother at the time, but something told me to answer,’’ says Bradley, who has an older sister and two older brothers. “My brother called me crying, like, ‘Mom is …’ I’m an hour into my drive from New York. So what’s that, three hours to go. I was with my wife, and I didn’t talk the whole drive. I probably went 100 miles per hour home. I tried to find a flight.’’

The flight was to Seattle, near his childhood home of Tacoma. A blood clot had struck down his mother, Alicia Jones. She was 46.

“When we had a problem, or if I had a bad game, I’m calling my mom,’’ Bradley says. “Because my mom, she was really our best friend. By the time I got there, she was basically gone. I was there with her in the hospital from the time I landed. I was there the whole time, in the same clothes, everything, for three days. I wasn’t eating. I wasn’t sleeping. I was just crying.’’

Then there was another panic, this time to return to Boston after his mother’s funeral.

“As I landed in Boston, my wife was delivering our baby,’’ Bradley says. “Her water broke at like 6:59. I landed at 7. So I landed and boom I went right to the hospital.’’

A new season was beginning and he was in need of perspective. Against the backdrop his mother’s death and the birth of Avery Bradley III – his first child was not yet a week old – Bradley arrived at training camp for his fourth NBA year amid the overhaul of the Celtics, who had traded Kevin Garnett and Paul Pierce while replacing Rivers with Stevens, who was entirely new to the NBA.

“When all the stuff was going on, he didn’t want to talk to anybody,’’ says Bradley’s best friend, Abdul Gaddy, who happened to be playing for the Celtics D-League team nearby in Portland, Maine. “He would be quiet for hours. He might just sit with you on the phone, or in the room.’’

At age 23, Bradley had a breakout season. His scoring average rose by more than 50 percent to 14.9 points, he became the best 3-point shooter (39.5) among those Celtics who played more than 30 games, and he maintained his high standards defensively. All of this he managed while wearing the emotional mask that hides his feelings from all but a few of those closest to him. It turns out that his distinctive approach to basketball had prepared him for the misery and the bliss of that difficult year.

“I kept to myself a lot more,’’ Bradley says. “I was more serious. I was very hard on myself. All that stuff is what drove me to prove people wrong even more. Like even still today, I get shots up after and before practice because I want to prove people wrong. But I know it takes hard work. I have to work hard.’’

The day when something clicked

“I first got to know him when he moved back from Texas,’’ says Gaddy. “He tried out for our AAU team, and I was the best player on the team at the time.’’

After three years in Arlington, Texas, Bradley and his siblings had moved back home to Tacoma with their mother. Their divorced father, Avery Bradley Sr., was a sergeant in the military. Bradley was a hyper-athletic eighth-grader lacking in skills when he tried out for the AAU team that featured Gaddy as well as Isaiah Thomas, the All-Star point guard who starts now in the Celtics’ backcourt alongside Bradley.

“My best friend used to make fun of me about the camps I wasn’t invited to, and I used to get mad,’’ says Bradley of Gaddy. “He was just always better, always the favorite. I was always the one in the shadow that everybody was like, ‘He’s not good enough. Might not even make it to college.’’’

“When we were younger, I had a flair and cockiness, and I carried that with me,’’ Gaddy says. “I knew that he loved me for it but hated me for it. I used to pick on him – ‘I got all the accolades, I’m the better-skilled player, I go to all these camps.’ He would beat up on me, because he was older and stronger. On the court we weren’t friends at all, but off the court …’’

They were the closest of friends, and Bradley would not enable his self-loathing to poison the friendship.

“I’m the oldest in my family, but growing up I was young for my grade,’’ Gaddy says. “He was the older brother I never had. He was always protective. I’m this skinny, scrawny kid, and I remember twice on the (AAU) circuit I got into it with somebody – the guy was talking about fighting me, and Avery was like, ‘Nah, you going to fight me.’’’

Did the opposing player back down?

“For sure,’’ Gaddy says. “Because he always has this look. He’s like that to this day: ‘Brah, I got you, I’m going to take care of you.’’’

“Growing up I was a different person than I am now,’’ Bradley says. “Now I’m the quiet, laid-back one, but I used to be the wild one in the group. I was like the bully. I got in a lot of fights growing up, and not just basketball fights.’’

Bradley used to beat himself up more often than any opponent on the court or in the street. One decade ago he declared his early retirement from basketball just as Gaddy, his AAU roommate on the road, was emerging as a future star.

“I remember one day after summer basketball, I called my AAU coach and I was like, ‘I’m done.’ Like, ‘Basketball is probably not for me,’’’ Bradley recalls. “I was 15, 16 years old. I told him that because the rankings had came out and I wasn’t even on them. My best friend (Gaddy) was No. 10 in the nation. He was the No. 2 point guard after John Wall. All of that hard work I’m putting in and it’s not showing.’’

His coach, Garry Ward, would have none of it.

“He told me I needed to work even harder,’’ Bradley says. “He was like, ‘I’m going to work out with you every single day.’ I was in the gym every day because I couldn’t shoot. I did fullcourt pullup jumpers every day, and that’s when it clicked with me. From that day on I wanted to prove everybody wrong.’’

He had discovered a formula of self-deprecation that worked for him. For his senior year of high school he was transferring to Findlay Prep in Las Vegas, which Bradley led to the national championship on his way to becoming Parade Magazine’s Player Of The Year. The explosive dunker, having rounded out his game, can see now that he hadn’t actually wanted to quit at all.

“Yeah,’’ admits Bradley. “It was a cry for help.’’

For all those who look up to NBA players with envy of their skills and rewards, the lesson is that it is neither as easy nor as joyous as Bradley makes it look. He is emerging as a star for the Celtics because for most of his basketball life he has looked in the mirror and not liked what he has seen. He has been harder on himself than any of his coaches or rivals.

“It’s kind of like he has an Army mentality,’’ says Bradley’s closest friend, who has seen their rivalry flip upside-down. Gaddy, betrayed by the AAU rankings at an age when potential must be nurtured and squeezed, would play four years at Washington and go undrafted. He is now starting at point guard for the club VEF Riga in Latvia.

Taking nothing for granted

After spending his requisite NCAA season at Texas, Bradley was expected to be picked among Nos. 10-15 in the 2010 Draft. Instead, his stock dropped after a workout with Oklahoma City, where he suffered an ankle injury that would require surgery. He now considers that setback to have been part of his good fortune.

“If I didn’t break my ankle, I was going to be a top pick,’’ Bradley says. “I probably would’ve ended up being in the lottery – and played point guard, and not been what people thought I was supposed to be. And then I could be out of the NBA.’’

He takes nothing for granted. After being sidelined from training camp, Bradley was introduced to the NBA by the highly-demanding Rivers and his Hall-of-Famers, in particular Garnett and Pierce. “It was hard,’’ says Bradley, “but it created a tough skin for me. I was able to take criticism and learn how to be a professional. It was the perfect situation for me.

“I think of my entire career – my life – like that. I came in here, I was injured, didn’t get an opportunity. Just imagine if I was given everything all at once? I might be out of the NBA right now. Same thing in high school: If I was the No. 1 player right off the bat, I might be overseas. I might have got comfortable.’’

Comfort is the enemy. Insecurity is his friend.

Told that Bradley believes he doubted his prospects, Rivers half agrees. “I didn’t know he would ever be the consistent shooter that he is now,’’ says Rivers, who is now coaching the Clippers. “Avery has become a great shooter, and that is rare. For him to go from being below-average to a great shooter does tell you how hard he works. He worked his butt off with us, but then you almost had to with Kevin and Paul and that group.

“One thing I did tell him: ‘Your defense is of a high-level NBA player. Right away.’ That was obvious. Where he struggled early on was being a help/team defender, because he’d never had to do that before. But I knew he was going to be a defensive star. I know I’ve told him that before.’’

Rivers ranks Bradley among the top wing defenders in the league – a small group that includes Celtics teammate Marcus Smart, as Rivers sees it. “At the 1, 2 and 3, they have one of the top 10 defenders,’’ Rivers says, including small forward Jae Crowder of the Celtics. “No other team can claim that.’’

Bradley insists that his elder teammates made his life difficult. “He told me he was a rookie for three years,’’ says second-year guard Terry Rozier, who has become a protégé of Bradley’s. “He was even doing things for guys when he was starting. He was like, ‘Bro, I want to take a nap too before the game.’ And they were still making him do stuff.’’

“They were very hard on me,’’ Bradley says of Garnett and Pierce in particular. “Very hard on me.’’

But Ainge holds to another point of view. “I don’t think that environment was conducive for the weak of heart,’’ he agrees with a laugh. “But I found out what our veteran players thought of him. When Avery started playing, he won his teammates over very, very quickly, just by his effort and intensity.’’

“I don’t know about that,’’ counters Bradley. “I mean, I was really close to those guys, they were like my brothers, and I didn’t get that sense from them. At first they more felt like I wasn’t an NBA player. I went to the D-League (as a rookie) and when I came back, I think that’s when I made them a believer. My first practice back, I had a nasty dunk that ended practice, and I think right then and there my mindset changed the way everybody thought about me. Doc was always on me. My teammates were always on me. And so when I came back from the D-League, it was like I was a different person.’’

Bradley’s potential became obvious to everyone but him midway through his second season, when he replaced Ray Allen in the starting lineup.

“(Rajon) Rondo, Avery, K.G., Brandon Bass and Paul Pierce – that was the highest-rated lineup in the NBA for the last 40 games of the regular season,’’ says Ainge. And months earlier, when Bradley courageously played through recurring shoulder separations – popping the shoulder back into place mid-game like Mel Gibson’s maniacal character in the Lethal Weapon movies – it was the elder Celtics who urged their rookie teammate to withdraw.

“I was going to keep playing,’’ acknowledges Bradley, who underwent shoulder surgery that spring. “But it was K.G. and them – they told me I needed to be smart about my career.’’

“He obviously has proven to himself and the whole world how wrong he was by that self-doubt,’’ says Ainge. “I can relate a little bit to that, being a player: When you don’t get the opportunities to play, you do wonder. It’s not common to admit to it, like Avery is doing here. But it is common to think that way.’’

Leading by example

On the day of each home game, Bradley arrives at TD Garden by 2:30 p.m. to stretch, meditate, and prepare. “That’s K.G. and Larry (Bird) type stuff,’’ says Ainge.

“I just like being here,’’ Bradley says. “It’s usually me, Brad and three video guys. My wife will pack me some food. I eat my food here, I chill with the guys. I feel like it gets me ready for the game.’’

It is an example of Bradley’s approach to leadership. He prefers to show the way forward, but if a scolding or pep talk is necessary, then he will pull the teammate aside for a private conversation.

Garnett and Pierce used to be less discreet. “They would call people out, and I could take that,’’ says Bradley. “But I know everybody else can’t take it, if somebody were to speak to them like that. I’m more going to take you to the side and, ‘You’ve got to do it like this …’ This is my second family, we are together every single day, and I want to see them be successful.’’

“He’s one of the better leaders that I’ve ever dealt with in my life,’’ says Rozier of Bradley. “He doesn’t care how mad I am at times. If he feels like he has to say something to me, he knows it’s going to help me. He reminds me that when the coaches say something, it’s not a personal thing.’’

It’s as if Bradley is mirroring the career path of Kawhi Leonard, who is five inches taller and has been surrounded by superior talent in San Antonio. And yet the similarities are striking, as Bradley’s high school teammate Cory Joseph – a former Spur – has pointed out to him: Both were picked outside the lottery, both have branched out their games from a defensive foundation, and neither of them seeks attention.

“When you find players that are true two-way players, it’s pretty rare,’’ says Spurs coach Gregg Popovich. “A coach can’t make that happen in somebody. They either do it or they don’t, and most don’t. It’s up to that individual who has the character to want to reach a certain level of competence at both ends of the floor. Avery is one of them, Kawhi is another one of them, and it is a coach’s dream when you have somebody like that.’’

Stevens agrees. “He’s very conscientious,’’ he says of Bradley. “He really thinks things through, and at the same time he has a unique ability to step up and play at a high level against the very best players. A lot of guys will taste a little bit of success and plateau. He continues to go up.’’

Told that Bradley has doubted whether Stevens believed in him, the coach can’t hide his surprise. “Ha!’’ says Stevens, and then deflects with humor. “I think he’s a really good player. Hopefully his minutes speak to that.’’

Last season Bradley hired agent Rob Pelinka, who is expected to aggressively pursue a huge raise when his four-year, $32 million contract expires after next season. Pelinka has joined Bradley’s wife and athletic trainer Tim Grover in urging him to recognize and draw strength from the investments he has made in himself.

“I want to just be respected,’’ Bradley says. “I’ve always been the quiet guy that doesn’t really say much. I just come in, I do my job and that’s it. But I want people to realize that I’m not a joke at either end of the floor. Every single time you play against me, you’re going to hate it.’’

Ainge believes Bradley should be an All-Star. “If I’m not an All-Star, then I need to (win) Most Improved,’’ Bradley says. “I work hard every single year. I watch film of myself, and no one is guarding superstars the way I guard them. I’m guarding these guys, and then they’re not guarding me.’’

Over the last couple of years Bradley has learned to be less negative – or to at least temper his approach with positive thoughts. Jeff Teague, who played with swagger during his 2014-15 All-Star season in Atlanta, provided one example. Another was drawn from Bradley’s former and current teammate, Thomas, who at 5-9 became an All-Star last year. “You can just tell when someone is confident in their game, and I think that is part of Isaiah’s success,’’ Bradley says. “He’s out there making it happen for himself because he believes in Isaiah.’’

“At this level, if you want to be really good, you can’t worry about what anybody else says,’’ says Thomas. “I think that’s what he has gotten better at, especially this year. Even if he’s not playing too well, he’s got a great attitude, he’s not getting down on himself and he’s just being positive.’’

They’ve always been opposites: Thomas the offensive extrovert, and Bradley the introverted defender who dwells and agonizes. “I go for it,’’ Thomas says simply. “He kind of lays back, checks the scenery out and then he will go deep into it.’’

Bradley’s is the harder line.

“It is,’’ says Thomas. “But that’s his way.’’

Ian Thomsen has covered the NBA since 2000. You can e-mail him here, find his archive here or follow him on Twitter.

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