Rajon Rondo’s claims of locker room dissension make sense. A whole lot of sense. How else could the Celtics have fallen apart so quickly, so drastically?

United we stand. Divided we fall.

You could blame it on injuries. Or age. Or the Goose. Or the Henny. But if you blame it on any of those things, you’d be forgetting this:

When the Celtics’ won 14 of 15 games earlier this season –and 23 of their first 28 — they were just as old, almost as injured, and had the exact same core of players. You can say what you want about KG being more banged-up now, but he wasn’t exactly moving around like Lebron James at the beginning of the year. Ray Allen and Rasheed Wallace aren’t shooting well now, but they weren’t exactly lighting the world on fire during the season’s first 30 games. Wear and tear is the biggest reason most people offer for the sudden swoon, but the Celtics didn’t suddenly get old overnight. Nobody got a few years older in the middle of the season.

Individually, the older Celtics — the Celtics whose dropoff is allegedly to blame for the poor play — are all operating at more or less the same levels they have all season. Paul Pierce, Kevin Garnett, Ray Allen, Rasheed Wallace… those old bucks are all producing at more or less the same clip as they have all year long.

Then what’s the goddamn problem?

‘It.’ The magical word.

Some teams have ‘it.’ Other teams don’t. Some teams search for it for an entire season, finally finding it in time to piece together a late run. Other teams never find it at all.

‘It’ can be tough to describe. To use a cliche, you might say it allows a team to play greater than the sum of its parts. ‘It’ is the ability to play together, to allow each player’s flaws to be hidden and strengths to be magnified. To rally around your team, no matter what the circumstances, and play inspired basketball. To know your team always has a chance to win a game.  To expect to win each and every game, but never take wins for granted.

At one point this season, the Celtics had ‘it.’ Remember Orlando on Christmas Day? With Paul Pierce out, that game should never have been won. On the road, in a hostile environment, sans their leading scorer, Boston should have been trounced. But they weren’t.

Instead, Boston clawed their way to a gritty victory. Pierce was out… So what? Tony Allen played great in his absence. Kendrick Perkins battled foul trouble… Who cared? Rasheed Wallace shut down Dwight Howard and contributed 11 points and 8 rebounds of his own. Kevin Garnett shot only 3-9 from the field… Didn’t matter. The Celtics’ defense held Orlando’s offense to only 77 points.

The C’s were on a mission and weren’t going to let injuries, poor shooting, age, or foul trouble stop them. At that time, there was no doubt: They had ‘it.’

Sadly, that Orlando game is the last time I can look back on a game and say to myself, “Man, the Celtics brought their ‘A’ game that night.” Since then, the wheels have fallen off. First, Baron Davis hit his buzzer-beater. Then, before you know it, the Celtics had lost 11 out of 17 games. They patched together three separate three-game losing streaks. Doc Rivers tried to dispel the notion that the sky had fallen, but for those 17 games it wasn’t nearly as high as it should have been.

The Celtics are now searching for answers. They’re searching to regain the magical ‘it.’

According to Rondo, they can start by looking in the mirror.

“You know, I think if we all had the right spirit,” he said, “as far as one goal, one thing in common, I think we’d be a lot better.”

Rondo asserted that the locker room has become a little divided.

“In the locker room, you can feel it,” he said. “You don’t feel like it’s the same continuity and camaraderie in the locker room as it was the first year. The first year, it was a crazy spirit in the locker room. But now it doesn’t feel the same. It’s not the same right now. We’ve got to find a way to get that back somehow, some way.”

What has happened in the locker room has transferred over onto the court. Boston hasn’t put forth a full 48 minutes of effort in God knows how long. They have gone through periods of painful execution that, for a team consisting of the exact same starters as two seasons ago, can be confounding. Both offensively and defensively, the Celtics’ teamwork that was once off the charts can go through spells of being very below-average.

“I can’t really elaborate on it too much,” Rondo said, “but I think we’ve just got to be a team with no agendas. We’ve got to play unselfish, you know? That’s on defense and offense.”

Playing unselfish basketball has no age boundaries. You don’t lose the ability to play unselfishly just because you’re within two decades of receiving an AARP card. You don’t get too old to execute the play. Or to rotate defensively. Or to dive on the floor after a loose ball. Every player on the Celtics , no matter how big his knee braces may be, should be capable of putting aside his agendas and putting the team first.

For the old, banged-up Celtics, playing may be painful. But for their fans, watching the way they’ve played recently hurts just as badly.

Unfortunately, ‘it’ can be elusive.