After a triumph of such fluctuating fortunes, and with such an incredible crescendo, you search for the difference. The act of skill or heroism; the piece of sheer good luck. The moment that left the Swans in unimaginable ecstasy, and the Hawks prone on the turf.
Adam Goodes's shot that, in agonising slow motion, dribbled the right way. The kamikaze defenders who swarmed on the ball, and their opponents, as Hawthorn laid siege. Hawthorn's Jack Gunston hitting the post, and Brad Sewell missing two difficult snaps that could have put a dagger in Sydney's heart. Nick Malceski landing the killer blow. Careers reduced to excruciating moments. Decisions made under incredible duress that echo down the ages.
In those last 10 minutes, the Swans were subjected to the most onerous test of mind and body imaginable. That they passed, with honours, makes this victory as sweet as any in recent memory - perhaps greater than their famous drought-breaking premiership of 2005.
Before yesterday's savage conflict, the very idea was red and white heresy. But these Swans had to survive a tortuous finale against desperate, seasoned opponents. Twice Sydney had stared into the abyss.
At quarter-time they trailed by 19 points. It would have been 25 had the siren not sounded just before the Hawks tried for another goal. Hawthorn are ruthless frontrunners. Buddy Franklin had overcome his early yips and hit the scoreboard. The talk was of a blowout.
That the Swans kicked the next eight goals, and built a 28-point lead 10 minutes into the third quarter, was not merely a consequence of their famous resilience, but a demonstration of the class some of us had underestimated. The relentless run of Dan Hannebery, Ryan O'Keefe and Lewis Jetta. The finishing skills of the recycled Tiger Mitch Morton. This was what the Swans could do when let off the leash.
Yet, just as Hawthorn's attack looked hopelessly constipated, the Swans were tested again. The Hawks kicked seven of the next eight goals - the lone Swans goal the result of a 50-metre penalty that Hawthorn captain Sam Mitchell will long lament.
Sydney's reaction? A period of sheer bloody-mindedness that, slowly but surely, dragged a Hawthorn team that was only one straight victory from footballing nirvana back into a competitive furnace. Back into the type of brutal contest the Swans thrive on: 10 minutes of sweat and grind that turned a team from gallant competitors to heroic premiers.
As the Swans collected their spoils, it was great stories, not merely great players, who strode onto the stage. Kieren Jack, the son of rugby league great Garry. Mike Pyke, the Canadian rugby player who had emailed a highlights reel to the club. Lewis Roberts-Thomson, the graduate of a great rugby school who is now a dual premiership player. Rhyce Shaw, Shane Mumford, Josh Kennedy and Ted Richards, who had vindicated moves from successful clubs.
Most poignantly, there was co-captain Jarrad McVeigh, who this time last year mourned the death of his baby girl. ''This is going to be the best month of our lives,'' said McVeigh, before lifting the premiership cup.
For coach John Longmire, who had the potentially awkward task of succeeding the universally respected Paul Roos, there was vindication and reflection. ''Mum, I hope you enjoyed the game,'' he said, having lost his mother during the season.
The Swans will say they worked and trained only for success. Yet there was a sense of astonishment at what they had accomplished. Did we do it?
Doubtless, Hawthorn will rue this as a grand final that got away. They squandered chances created by their midfield. Franklin kicked 3.4 and sprayed another two shots out on the full. They were dire in the second quarter, kicking just one point as the Swans piled on six goals. But Hawthorn did not lose this game, it was taken from them. Twice in this arm wrestle the Swans' twitching arms were bent backwards. Twice they muscled their way back.
Now, against the odds, they are premiers. Not by luck, by sheer bloody willpower. Their celebrations are richly deserved. Norm Smith medallist O'Keefe issued the instructions: ''To my boys, run amok.''