On this occasion, it was bitter disappointment and it was raw.
It still is.
Two weeks on the frustration and the hurt still dominates. There is an almost 30-year association with Sunderland to reflect on but for the most part, that will have to be for another time.
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Whether it be the past, the present or the future, any discussion for now ends up back at that disappointment.
“It hurts, really hurts,” he says.
“I've not processed the disappointment, that's for sure.
“I think it'll take a couple of years for that. The hurt will always be there, at not being able to achieve what I wanted to achieve.”
When he returned to the club in 2019 he had already been in the game long enough to know that in this sport, you can’t always get what you want.
But the sense of unfinished business was overwhelming. He had ridden the crest of a wave before, both here and at Middlesbrough, and this was a precious opportunity to try and do it one more time.
There was no naivety, but there was hope.
Leadbitter is a deep thinker about the game, and the last two-and-a-half years have taught him a ‘hell of a lot’.
There have been many, many lessons learned, many notes taken.
Some fine days along the way, too.
A Wembley win, for one, and there is unmistakable pride that despite many believing his career could be over, he played almost 50 games this season and to some level, too. When he was not in Sunderland’s midfield, you noticed.
That overall disappointment, though, is a reflection of the mentality that has delivered nearly two decades at the top of the game.
The belief that the only thing more important than winning is winning the next one, and that each and every game is defined by the preparation done.
At times you wonder if that mentality is a double-edged sword, one that drives success but leaves little time to dwell on it.
“Yeah, I think it probably is,” he responds.
“I've always been driven by standards.
“That's a big part of my life and a big factor in that is that I was brought up by Roy Keane. That becomes instilled inside of you and that lasts for the rest of your career.
“I believe that's the way football should be done, every day, not just days you choose. That's how you're successful.
“Roy Keane won everything there was to win at a massive club, and I spent three years with Aitor Karanka who had done it at Real Madrid.
“They both had that similar vibe.
“Whenever I speak to younger players I always say, I think it's about Monday to Friday and what you do then, and then Saturdays should become easy.
"One thing I think when you look back, is you wish you'd enjoyed those moments a bit more.
“But what you focus on is the next game, the next training session. Roy instilled that in us and for me that's the best mentality you can have.
“They were good times and that spell probably made my career, that chance Roy gave me.”
There is, without doubt, a lesson here as Sunderland face up to a fourth season in League One.
“It's something I hope I've passed on,” he says.
“That calmness if you like, even when you win games and especially when you're Sunderland in League One.
“It's tough in this league because everyone wants to beat you but when you win, it's about the next game and it has to be about the next game.”
Sunderland look to be on the brink of a major rebuild and that leaves Leadbitter looking to the future for the club he loves with optimism.
“You have to deserve to be where you want to be,” he says.
“I'm a big believer that in football, you get what you deserve.
“The football club, as a fan, it has to have a massive rebuild. I think that's good for the club, I really do. The club needs it, it needs a freshening up.
“I'm speaking as a player who has played for a lot of years and made a lot of appearances. I love Sunderland AFC and I think everyone knows it needs a rebuild, and hopefully the people doing that now are going to do that.”
If any word defines Sunderland during Leadbitter’s second spell it is instability, and the impact of that has been obvious.
“It's difficult for me to talk because I love the club but yeah, it's difficult for players to work under three managers in two years,” he says.
“Hopefully they've got a structure and a plan in place now, so that's not going to happen now.
“Jack Ross was very unfortunate, very unfortunate. Behind the scenes the work he did was outstanding for the football club. I only worked with him for six months and I saw what he dealt with.
“My whole time in football, I've never seen it where every single player has gone to the manager’s office when they leave. Staff, as well. He had a lot of respect at the club.
“Moving forward, I see young players at the club who need opportunity,” he adds.
“A run of 15, 20 games, game after game, they need that. I'm sure they'll get that and I'm pleased they'll get that because they're very good young players.
“The club needs, and I'm pretty sure it will get it with the plans in place, a full structure.
“You can't have short-term fixes and succeed, I've learned that in football.
“We've maybe tried to do that, chased the promotion and it didn't happen. I think the right thing for the club now is to do that proper planning, not just for next year but for the next five, ten years.
“It needs an identity back.
“I'm confident Lee Johnson will take the club forward.
“He's been good with me and he has an identity for how he wants to take the club and team forward.”
The outpouring of emotion that greeted news of Leadbitter’s departure reflected the impact he has had even during what has been a difficult time for the club.
His play-off performances in the very toughest of times two years ago will live long in the memory of all who witnessed it, while his consistency since taking time away from the game has been inspirational to so many.
He has shown that it’s OK to be affected by grief, and that you can come through it.
It still affects him now, but the messages of support from right across the region have helped and so too have been those who have taken strength from his journey.
It’s a spell of his career he reflects on with pride, even amid the disappointment.
“It's well documented that a lot of people wrote me off when I went through a period where not many knew what was going on in my life,” he says.
“That's one thing, it's probably one of the things that I'm proudest of in my career, to be honest, to come back from that.
“I always backed myself.
“I could easily have walked away but I didn't want it to end that way, it wasn't the right way.
“I'm proud of the way I came back.
“I always knew Phil Parkinson would have to put me in the side and I told him that,” he adds.
“I knew that because I was in a better place and my performance in pre-season reflected that.
“It was a matter of time and as a professional footballer you've got to back yourself, and I did that.
“But you always dwell on disappointments, and that's what drives me on in my life really.
“Ultimately, I didn’t achieve what I wanted to achieve during my second spell at Sunderland.”
Leadbitter defines himself as someone who tries to do things properly, to just get on with things.
So when he says that he will not commit to his next step until he is certain it is the right one, you believe it.
But here’s the thing.
The passion with which he stills speaks about the game, about Sunderland and Middlesbrough, about standards and youth development and coaching and learning and everything in between, tells you how much he has to offer.
For now the disappointment may still feel a little overwhelming, but whether off the pitch or on it, this story still has a lot of chapters left to be written.