The Brisbane Lions mentor had already decided to quit weeks earlier, telling club hierarchy of his plans after a loss to Sydney to begin their AFL finals campaign.
Fagan, conscious of his message "wearing thin", had even thought about stepping down after their first premiership in 2024.
But a rule he stuck by at both Melbourne and Hawthorn remained central in his thoughts and kept him at Springfield for another two seasons, netting two more premierships.
"I've got this silly rule in my head, the 10-year rule," the 65-year-old, who had a season remaining on his contract, said on Thursday after an emotional address to players and staff.
"I reckon that's about how long you've got in the place to make a difference, and then it's time to move on."
A teacher and state-league player from Tasmania, Fagan spent 10 years in various coaching and football roles at Melbourne before a trophy-laden nine-year stint at Hawthorn in a wide range of roles.
"It was a punt (from Brisbane); I wasn't a big name in AFL footy and most of the players didn't know who I was when I first turned up," he said.
Now counted as "sons", Fagan couldn't tell if the players were emotional on Thursday because of the tears in his own eyes.
"When you spend a long time with a group, like I have with this group, the message can wear thin," he said.
"It hasn't yet, obviously, but I don't want to be around when it does."
He said the prospect of a four-peat, unseen in the VFL/AFL since Collingwood from 1927-30, was a "club thing, not a Chris Fagan thing".
"I wasn't swayed by that; I'm not that into history," he said.
"For too many coaches sort of it ends up in tears. Not like the tears today, they were happy tears.
"Being an AFL coach is relentless ... eat, sleep, and breathe every day of the year.
"And I've just got to the stage where I just don't want to do that anymore."
Brisbane won just 10 games across Fagan's first two seasons but the coach finished with a better win-loss record than fellow three-peat mentor Leigh Matthews.
And he said their great escape on Saturday, engineered as he was drafting his "loser speech" in his head, would not be topped.
"I am never going to forget that, and I'm going to watch it over and over and over again ... made the boys watch it this afternoon," he said.
"Funnily enough, the last five minutes I coach were the best of my life."
Long-serving chairman Andrew Wellington praised the coach's humility in labelling him "one of the great AFL coaches in the history of our game".
Fagan will return to Melbourne to be close to his family but wants to remain in the football industry and have no say in who takes over at Springfield next season.
He does hope his rise from relative obscurity is heeded, though.
"I'm pretty sure there's other people out there that are like me that have probably got the talent and the abilities to do a coaching job, but don't get looked at," he said.
"I just hope it opens up a few eyes. That's what I hope for."
Brisbane football boss Danny Daly, who left a career in banking to join Collingwood in 2000 before stints at North Melbourne and Richmond, has confirmed a desire to become a senior coach.
He has previously knocked back interest from Gold Coast, Collingwood, Essendon, West Coast and Melbourne.
Assistants Dale Morris and Cam Bruce have also been floated by both Fagan and Daly as capable options.
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