The All-Star pairing of LeBron James and Kyrie Irving, a duo that complemented each other so beautifully, lasted just three seasons.

It seemed like a partnership that was destined for more, despite three trips to the Finals and a 2016 championship for the Cleveland Cavaliers.

The reason for the divorce has been well-documented: Irving wanted his own team, out of James' enormous shadow and the opportunity to be more Michael Jordan than Scottie Pippen.

Now that he's gotten his wish on an underperforming Boston Celtics team, Irving has predictably gained more appreciation for everything James did as a leader.

"I had to call [LeBron] and tell him I apologized for being that young player that wanted everything at his fingertips, and I wanted everything at my threshold," Irving told reporters Wednesday night. "I wanted to be the guy that led us to a championship. I wanted to be the leader. I wanted to be all that, and the responsibility of being the best in the world and leading your team is something that is not meant for many people."

For Irving, this was a big step toward becoming the leader he wanted to be. For James, perhaps some frustration over what could have been mixed with the satisfaction of knowing he may have finally gotten through to his most prized pupil.

For Cavs fans, it's just another kick in the teeth after watching Irving and James leave in back-to-back years, now stuck watching the NBA's worst team yet again.

Irving thought he was ready for such a leadership responsibility, which isn't surprising given his first few years in the league. It's also not surprising how much more he has to grow. To find answers for both, we need only dive into his past.

Why Kyrie Thought He Was Ready

Before James returned to Cleveland in 2014, Irving enjoyed signifiant individual success while the Cavs continued to fall short of the postseason. 

When James left in 2010, the Cavs plunged from 61 wins to 19. Any potential faces of the franchise were too old (Antawn Jamison, 34), too young (JJ Hickson, 22) or were traded away (Mo Williams) midseason.

Whatever lottery pick coming in 2011 would be the new leader, ready or not.

Enter Irving, all of 19 the day of his NBA debut. Cleveland wasn't going to bring in any star free agents to save the franchise. This was Irving's team for as far as he could take it.

What followed was a textbook lesson on how not to grow a star.

The Cavs won just 21 and 24 games respectively in Irving's first two seasons under head coach Byron Scott. Neither year did the team bring in a veteran point guard to help mentor its budding floor general, instead using the roster spot to take fliers on guys like Donald Sloan, Jeremy Pargo and Lester Hudson.

The Cavs removed most of the adults from the room, trying to strike it rich with low-ceiling prospects rather than adding veterans with championship experience.

Irving didn't have anyone to show him how to lead. No one to show him how a championship-caliber point guard practices, prepares and plays. If he turned the ball over multiple times and gave a half-ass defensive effort, who was Scott going to put in over him? The accountability put forth by the organization was severely lacking.

Firing Scott after Irving's second year wasn't surprising given Cleveland's record, but replacing him with Mike Brown was.

Brown spent five seasons coaching James with the Cavs, and while he got the team's best defensive effort, he was notorious for failing to hold James accountable in practices and video sessions. Cleveland was finally supposed to ease the burden on Irving in year three, although the hiring of a defensive-minded coach seemed to stunt his growth.

Irving's scoring numbers plummeted under Brown; Anthony Bennett quickly became a bust of a No. 1 overall pick; and Andrew Bynum, the Cavs' biggest free-agent signing at the time with Irving, flopped and was traded shortly after Christmas.

Brown even advocated that the Cavaliers try to trade Irving before the team fired him in the offseason instead.

There Irving stood. Still just 22 years old and about to meet his third head coach in four seasons. Dozens of teammates already shuffled in and out, none of whom could help him carry the team.

The Cavaliers had given him no choice but to lead, no matter how many mistakes were made around him.

What Kyrie Can Still Learn From LeBron

Despite how good the Celtics could wind up being under Irving, leaving the NBA's best player and a near-guaranteed trip to the Finals every year was a mistake. At least during the time he did it.

"Kyrie knows he left a year early," a key player from those Cavs teams told Joe Vardon of The Athletic. "We were supposed to take another run at it [last season] and then take a look at everything."

Irving, 26, still has a lot of room for growth as the leader of the Celtics. For perspective, he's still a year younger than James was when the four-time MVP won his first championship. James' time with the Miami Heat was his transformation stage.

He had to be in a championship culture with veteran teammates to truly become the leader he would later become to Irving in Cleveland. Having two All-Stars (and a Finals MVP) in Dwyane Wade and Chris Bosh didn't hurt, either.

There is no one to match Wade's star power on Boston's roster to help ease the burden on Irving. Is there even anyone as good as Bosh?

What James mastered in his second Cavs tenure was the art of delegating responsibilities to teammates and putting them in the best possible positions to succeed.

He could read the defense like a quarterback, throwing no-look darts to open shooters or cutters who slipped behind their man. He was perfectly fine putting the ball in Irving's hands in clutch situations or taking over himself. He knew everyone's role and could explain plays from all five positions.

"[LeBron] was one of those guys who came to Cleveland and tried to show us how to win a championship, and it was hard for him, and sometimes getting the most out of the group is not the easiest thing in the world," Irving told reporters on Wednesday.

James has already laid the groundwork for what Irving needs to do (and some things he shouldn't) from their time spent together.

For example, he set the tone in the training camp of 2014, calling a 30-minute players-only meeting to break down every expectation he had from each teammate, even those who weren't likely to make the final roster. This act of inclusiveness is something Irving has struggled with, especially with his recent harshness toward younger teammates:

"I did a poor job of setting an example for these guys of what it's like to get something out of your teammates. You go and you say something publicly, and it ends up received in so many different ways, and you never know how fragile or what guys are going through when you say things like that. You're expecting results, but at the same time, I should've kept it in-house.

"Going forward, I want to test these young guys, but I can't be a bully like that. I want to get the best out of them, but I can't do it personally like that. That was a learning experience for me of being in this position of really realizing the magnitude of my voice and what I really mean to these guys. I want to see them do well and do that where I empowered them."

This is where James and Irving have shared similar leadership qualities. James made a mess of his fit in/fit out tweets directed toward Kevin Love, something he should have handled in the locker room and kept off social media.

He also has a habit of referring to younger teammates as "kids," something Irving himself didn't seem to like. While both Irving and James' intentions may have been good, sometimes perceived motivation can come off as humiliation. Irving needs to make sure he doesn't cross that line, especially still being so young himself.

Irving does carry perhaps the greatest symbol of leadership: the championship ring he and James won together. One that, at the time, felt like just the beginning.

Don't blame Irving for thinking he didn't need James to win or for not being receptive enough to his words when they were together. That's just how he was raised in the NBA, with constant change swirling around him and the required leadership persona he had adopted.

Did Irving leave James' guidance a little early? Probably.

Is he finally ready to lead a team? Who knows.

Greg Swartz covers the NBA for Bleacher Report. Follow him on Twitter.