It's only when an Alex Ferguson or a Jim Gavin move on that their brilliance is appreciated

It is an axiom with which disciples of Alex Ferguson, Jurgen Klopp, Pep Guardiola, or closer to home, Dublin’s old North Star, Jim Gavin, will be intimately familiar.

A transcendent manager is first and foremost an impenetrable shield: Against the asteroid of falling standards; the crater-gouging debris of dressing-room cliques, training-ground apathy, or self-doubt; the celestial grenades that pound morale, hunger, and self-belief.

A firewall against the kind of terrible vision which loomed large and horrific on Sunday before an impotent Ralf Rangnick.

The eminent leader’s greatest gift to his sporting flock is an ability to fatten the perilously thin line between abundance and ruin, making it appear wider than the Grand Canyon.

To make the brutally difficult seem absurdly straightforward.

Through force of personality, an aura that spreads to blanket an entire organisation in a cloak of invincibility, these once-in-a-generation chieftains arm supporters with an illusory conviction of glory without end, of a champagne and cigar eternity.

It is why the Stretford End continues to mourn Ferguson, Hill 16 craves the lost familiar of the Gavin era, while The Kop and The Etihad, even amid euphoric days of thunder, fret about life after Klopp and Guardiola.

Ferguson armed United with a conviction that they were immune to recession. Gavin presented an eloquent rebuke to the thesis that nothing can be forever.

They banished uncertainty.

They coaxed teams from a long malaise – Old Trafford waited 26 years for their 1993 league title, Dublin's 2011 All-Ireland under Pat Gilroy was only their second in nigh on three decades before the Gavin supremacy – and insulated their tribe against mortality’s shiver.

Klopp has lit a similar holy fire at Liverpool.

The charismatic German not only ended a 30-year wait for a league title, he did so while, in the words of writer James Gheerbant, plugging into the same “emotional circuitry” as the club’s supporters.

Klopp has reimagined Anfield as a palace of joy even while Old Trafford is force fed a bland, unpalatable, diet of a future stripped of the once familiar and flavour-rich certainties.

The latter serves as a cautionary tale to the former, a reminder to enjoy the transient ride across the sunlit uplands, because even the smoothest journey to the stars can fall into a terrible tailspin as soon as the pilot steps out of the cockpit.

Yes, the best of the memories may always be immune to the passing years, but the team itself can quickly age and wither when the manager who somehow held even time itself in a chokehold passes the baton to a mere mortal.

A team’s rising up is not entirely down to the figure in the dugout.

In the world where Liverpool and the Manchester goliaths operate, money, transfer-policy, structures, world class players and tradition play major roles in picking the locks to glory.

Gavin could call on once-in-a-century harvest of extraordinary talent. For a while it seemed that Dublin might have an endless supply of hall-of-famers on tap.

It is only when a Ferguson or a Gavin move on that the brilliant clarity of their navigation, along with the fragility of imperium, is revealed in grim shades.

The culture these superior leaders forge seems untouchable until it quickly fades, erodes, dims and turns to powder in their absence.

Manchester City might feel their oil money will carry them above the storm when Guardiola steps into the shadows.

But United have a net spend of a billion pounds on players since their Glasgow prince abdicated in the summer of 2013. They have bought Ballon d’Or recipients, World Cup winners, scoured the world, smashed transfer records.

Jose Mourinho won Champions Leagues with Porto and Inter, Louis Van Gaal with Ajax; between them, these iconic figures had won 15 league titles with eight clubs across seven countries.

Yet all the money, all the glittering coaching CVs and skyscraping egos did not even come close to reigniting the Ferguson flame.

Dublin stretched out the boundaries over six years of unprecedented achievement, yet without Gavin’s electrifying secret sauce they have resembled a decommissioned forcefield.

Might Liverpool, even petrodollar laden City, struggle for altitude when Klopp and Guardiola move on?

United and Dublin were polished to the highest gloss by figureheads who made the difficult pursuit of high-achievement seem as effortless as turning the pages of a favourite book.

As these celebrated teams’ current limpness illustrate, if it is ferociously difficult to reach the mountain top, it is harder again to make a long-term home there while every sniper has the bull’s-eye on your chest in his crosshairs.

In his latest novel, The Magician, Colm Tóibín talks of the "hard and hidden place where a subject was lured towards the light in a process that was like alchemy".

He is referring to a novelists task into seeking to construct words into sentences into chapters into some towering finished work.

But he might also be shining a light on the process undertaken by a Ferguson or a Klopp in transforming a vision into something immense and unforgettable.

Every syllable in the story of a football club’s days of grandeur ought to be savoured by its congregation of devotees.

Because the ending, unexpected and numbing, can come like a bolt from the sky. And leave even the most faithful wondering if the sun will ever again rise.