Everyone has a theory for why the Boston Celtics' 2018-19 season went off the rails.
Some of those theories are more rational than others, and most (if not all) place at least some blame on Kyrie Irving.
But Marcus Smart may have just offered the most honest and eye-opening assessment yet of last season's talented but enigmatic squad.
Speaking to ESPN's Zach Lowe on Monday's episode of "The Lowe Post" podcast, Smart admitted last season's squad had trouble communicating with each other, especially when it came to off-court issues that several players were dealing with.
"I think it was just hard for everybody last year, including myself," Smart told Lowe. "I was dealing with my mom's passing, and everybody had their own little individual things they were dealing with.
"(So) when it came to the team, it was like, 'Eh, oh well. I've got more things I'm stressed about that I need to be focused on right now individually.' And the team kind of got put on the back shelf."
Smart's mother died shortly before the 2018-19 season began in September 2018, while Irving lost his grandfather just over a month later. Irving recently said his grandfather's passing weighed heavily on him, and Smart suggested that's in part because the Celtics weren't comfortable bringing their private struggles out into the open.
Boston Celtics
"You were afraid to talk. You didn't know how to talk to anybody," Smart said. "Growing up as young men, you're always taught that you don't want to show your emotions, you don't want to cry, and there's this stigma on it that as a man, you're supposed to be manly.
" ... Mental health is a big issue in a lot of sports, and that's what was going on. Instead of putting ourselves out there, everyone was holding it in."
Contrast that atmosphere to this season, where Smart says the vibe is much different.
"Now, everybody's mind is free. Everybody's confident, everybody believes more in themselves, and we're just having fun again," Smart said. "Whatever anybody individually was working on, instead of holding it in, we're now even talking to each other about it. We couldn't do that last year."
One could connect the dots to suggest Kemba Walker's addition and Irving's subtraction helped facilitate that change of mindset. But Smart insisted the culture shift was more the Celtics learning their lesson than any lack of leadership on Irving's part.
"I think last year just opened our eyes to the outcome of holding all that pent-up aggression or whatever you're going through inside. That doesn't work for us." Smart said. It's going to bring you down, and everyone hated feeling down."
"I'm cool with Kyrie, I'm still cool with Kyrie. ... As a friend, Kyrie is a great person. Kyrie had issues, we know, just like every last one of us. Kyrie had to go through some of the things he's never gone through alone, and he had to deal with it. He didn't know how to deal with it.
"It was his first time having his own team, not being with LeBron (James), not having somebody who's been bombarded with those things and knows what to say, what to do and how to do it. He had to deal with it on his own, just like everybody else, and that affected him as well."
The Celtics are tied for second place in the Eastern Conference at 11-4, so they're off to a good start in putting last season behind them.
Don’t miss NBC Sports Boston's coverage of Celtics-Kings, which tips off Monday at 7 p.m. ET with Celtics Pregame Live, then Mike & Tommy have the call of the game at 7:30 p.m. You can also stream the game through the MyTeams App.