Media day is a time for optimism. It is a time when everyone is in great shape, rookies always contribute and no one is unhappy with their roles.

Well, make that almost no one. Glen Davis took time to express uneasiness with his situation Monday, noting (correctly) that his role has changed every year that he’s been in the league and that he and Doc Rivers were “going to go through some ups and downs.”

Davis is in the final year of his contract, as is Kendrick Perkins, who also raised a few eyebrows by rather strenuously asserting his hold on the center position.

“My spot is not up for grabs,” Perkins said. “So, when I come back I will be in my spot. Everybody else will just have to adjust to me after that.”

Then Perkins made everyone laugh by objecting to the new rules on technical fouls.

“Do I look mad to you?” he asked a reporter. Yes, he was told. “But I ain’t mad though. That’s stereotyping.”

So it begins. They’re honest, unfiltered and sometimes funny as hell. The word that kept coming up Monday was “personality.” As in: The Celtics sure do have a lot of it.

KG, Shaq, Baby, Nate, Ray, Paul, Perk, Rondo and somewhere in the middle of it, the one named Doc will have to sort through it all and keep everyone on the same page.

“He’s the perfect coach for these guys,” Danny Ainge said. “They have strong personalities, but they want to be coached and I think they know they can’t do it on their own. They have to do it in a team concept. I think they have a lot of respect for Doc.”

This is true, but as Rivers said, “I hope it’s going to be easy. I have a feeling it’s not going to be.”

No, it’s not going to be easy. Not on the court where the Bucks and Hawks are still improving and the Bulls and Heat loaded up to varying degrees. That’s not even mentioning Orlando, long the preoccupation of the Celtics hierarchy.

“The East,” Kevin Garnett said, “is nice.”

And then there’s the Lakers.

“There’s 30 other teams and the Lakers are the defending champs,” Paul Pierce said after some Miami talk. “And nobody said nothing about the Lakers. That’s crazy.”

It won’t be easy in the locker room either, not with this many players who can contribute meaningful minutes and that many great (there’s that word again) personalities.

“Everybody says the right things in August,” Rivers has been saying since he arrived back in town.

It won’t be easy, but it will be a wild ride.

“It should be a fun year,” Garnett said, alluding to the whole NBA. “I can’t remember more of a soap opera type of season, other than when Diesel went to L.A. That was a real soap opera. Also when Gary [Payton] and Karl [Malone] went to L.A. That was real soap opera. Probably when Ray, myself and Paul got together, that was a bit of a soap opera. This is no different. It’s good.

“I’m happy for those guys,” Garnett continued. “I’m happy for them to be in situations that they want to be in. It’s always good to play with another guy that’s just as good as yourself. Takes the pressure off. That’s really what you want. When you sit back and watch Magic and Bird, they had the supporting cast so it’s good to play with guys just as good as yourself.”

Garnett was talking about the Heat, but in a way he could have been talking about his own team. They were the original thrown-together super team and now they have added more and more pieces to the puzzle.

There have been informal scrimmages taking place the last week or so. Garnett has been there, and so have Pierce and Allen, and the one player who has been getting out on the break.

That would be Shaq, and in a room full of personalities his is undoubtedly the biggest. That, and the other five things we learned:

SHAQ HEARS YOU

This is what happened when someone asked Shaquille O’Neal about the comments Kobe Bryant made after winning his fifth championship last season.

“Yeah, I heard it,” O’Neal said. “My whole career, I’ve been the measuring stick for excellence. It’s glad to see that I’m still relevant. I would have been more upset, more hurt if Tim Duncan had made the comment. I don’t compete with guards. They have the ball more than I do, they shoot way more than I do. I’m only competing with Tim Duncan. Hopefully I can get number five before Tim Duncan. Respectfully competing with Tim Duncan.”

So, there was that. He was also asked whether it motivates him that people question whether he can still be a contributor on a championship team. 

“I can remember a long time ago where I only wanted one [championship],” he said. “Now that I have four, if you think about all the great players that are in the league, no one’s going to catch the great Mr. Russell and the great Mr. Sam Jones. They’re not even in this conversation. Michael has six. Magic has five. Kobe has five. If I can catch up with those guys I’ll be satisfied with my career.”

If it hasn’t sunk in yet, Shaquille O’Neal is going to be playing for the Celtics. Reggie Jackson once said that he didn’t go to New York to be a star, he brought his star with him. That’s Shaq, although he wouldn’t have needed to say it, and he would have sounded ridiculous if he had. 

Instead he said this: “Whatever Doc needs me to do, that’s what I’m going to do. My first 17 years it was all about me, and scoring and now that part of my game is over. Now it’s on me to be a damn good role player. Whatever Doc and the city of Boston need me to do, that’s what I’m going to do.”

Shaq hears you. He hears all of it, from Kobe to the columnists to the fans who want him to accept his role. How this plays out will be the most fascinating subplot of the season.

THE CELTICS ARE EXPECTING BIG THINGS FROM KEVIN GARNETT

There’s this theory floating around that with a full season behind him following his knee surgery, Kevin Garnett is going to be more confident in his body, and therefore be more like the KG of years past.

As theories go, it’s not a bad one. Ray Allen remembers feeling slower and less explosive in the year following his ankle surgery. He also recalled feeling better the following year and even better the year after that.

Garnett himself noted that he didn’t feel 100 percent all of last season.

“No,” he said emphatically to the question. “No, I think more mentally than anything was hard for me because I was playing through some difficult times. I’m not one to make excuses. I’m not one to be out here [whining] and complaining about things.”

But this year?

“I feel very strong,” he said. “I feel very vibrant. I’m excited about the year. I’m totally embracing this and going to have some fun with it.”

You can make a case for this player or that player being the most important on the roster. The one they can’t win without. It’s impossible to know the answer for sure, but in the two years Garnett was able to play in the playoffs, the Celtics reached the Finals and in the one year he wasn’t, they lost in the conference semifinals.

Garnett is the key to their defensive schemes, especially with Perkins out, and their glue on offense. His optimism was the best note of the day for the Celtics.

DELONTE WEST IS GOING TO BE A MAJOR FACTOR

The tip-off came on Thursday when Ainge mentioned Delonte West several times before the team’s charity golf outing. This was Rivers Monday: “I don’t think I’ve ever coached a more competitive human being.”

West will have to sit out the first 10 games of the season to serve an NBA-ordered suspension, but when he is able to come back, the Celtics see him as a multiple-position defender and multi-talented guard.

“Delonte is huge for us because when you lose a guy like Tony Allen, he was our defensive stopper,” Pierce said. “Delonte is probably going to fill in that role. He brings some versatility to that position that we haven’t had since he left.”

They all wanted West back: Pierce, Perkins and Rondo. Truthfully, they never wanted him to leave and Ainge didn’t really want to give him up.

“If it wasn’t for such a good player it would have been very difficult for me to trade Delonte,” Ainge said, referencing the Ray Allen deal. “He’s a perfect fit for what we need.”

What they like best is his toughness.

“I wanted Delonte to come here right after he got waived,” Pierce said. “I love playing with guys like Delonte because you know he’s going to compete every night. You want those types of guys on your team.”

Until he does return there are minutes to be had at the backup wing spot. Von Wafer has the inside track right now, along with another player who also wasn’t so certain to be back: Marquis Daniels.

MARQUIS GETS A SECOND CHANCE

If there was an award for the most reserved Celtic personality, it would undoubtedly go to Marquis Daniels. Some mistake this for nonchalance, but that’s just his way.

“I’m a guy that doesn’t get high on the highs or low on the lows,” he said. “I just see it as another opportunity to come in and seize the moment.”

By now we all know the story. Daniels played well in the early part of the season, then he hurt his thumb and was never the same. He’s back because the Celtics feel like he’s the player he was early in the season.

Daniels said that his hand finally felt 100 percent better over the summer. He changed his number to eight, last worn by Antoine Walker, and spent a good part of the summer working on his jumpshot, particularly from behind the arc.

Don’t expect him to bust out a Walker shimmy in homage, but no, he doesn’t lack for confidence, nor did he lose it last season.

“I never lose that,” he said. 

On this team of last chances, Marquis Daniels gets something even rarer: a second one.

PEOPLE WILL LOVE JERMAINE O’NEAL

Jermaine O’Neal hated the Celtics. That’s what he said, but it is not exactly right. He hated playing the Celtics, except that’s not it either. To get O’Neal’s respect, he has to reach a level of what he termed hate during the time he’s on the court and the Celtics made him reach that point.

“At the end of the day it’s never personal,” he said. “You respect them. I always respect them. I look at big Perk like I looked at Udonis Haslem. Warriors that are going to suit up and play hard, and are not going to back down. Listen, you’re going to butt heads sometimes. You love the opportunity to get to play them.”

In any chaotic situation, a little balance must always be present and in the other O’Neal, the Celtics may have found a support beam. He talks softly and confidently and walks proudly and quietly. He’s the other O’Neal brother and that’s just fine with him. 

First, the injury stuff. He got kicked in the ankle late last season and wound up with a severely swollen ankle that left him ineffective in the playoffs.

“You don’t make any excuses,” he said. “Your team expects you to play hurt and if you don’t play, then you’ve got to take the brunt of whatever comes with it. If you can’t play, then you shouldn’t be out there. But I felt like I could help the team. It just didn’t work that way.”

How it worked out was O’Neal was one of the few players to actually leave Miami, and in his first experience in free agency, he elected to come to Boston.

“It means a lot to me,” he said. “I can’t picture a better place to end my ride than with a championship-caliber organization.”

He joins a massive front line with options upon options for Rivers to sort through and utilize. “The most intriguing part for me is I get to play alongside Shaq, KG, Big Baby, Perk,” O’Neal said. “More than anything, everyone’s willing and ready to sacrifice.” 

That’s the whole thing in a nutshell: A fascinating experiment involving uniquely talented individuals that also requires understanding and acceptance.

Or, as Kevin Garnett said, “I don’t like us. I love us.”