The pain of tonight may feel fresh, but we've been here before.
Eoin Hand's reign ended in a 4-1 hammering against Denmark in Dublin 4 back in 1985, as a brilliant Danish side exploited an Irish side playing an unfamiliar 3-5-2 formation. Hand admitted that he experimented with the lineup as there was nothing at stake, but his tinkering ended widening the chasm of class between the sides. Hand's plan was stupid, but it was at least a plan.
Tonight was an extraordinary, lamentable indictment of Martin O'Neill's management. After Ireland fell behind to Eriksen's wicked, brilliant goal to make it 2-1, Denmark sat back comfortably and watched the Irish side implode. They looked like a side who had never played together before, with sloppy passing and indecision met with tetchy exchanges between players. Brady admonished Harry Arter for taking too long to pass. Ciaran Clark berated Darren Randolph for not coming for a ball off his line. Clark himself heard some McClean caviling minutes earlier, for mindlessly knocking a ball out of play. McClean and Meyler collided in their own penalty area.
Soon, most accepted that Ireland needed to cling onto half-time for an opportunity to regroup. It is no exaggeration now to say that they would have been better served not trotting into the dressing rooms at all, as Martin O'Neill found a flame and doused it in petrol.
The manager panicked blindly, and gutted his entire midfield to bring on Wes Hoolahan and Aiden McGeady. The latter did not make sense: why have confidence in Callum O'Dowda for the away leg, and not play him here? O'Neill made those subs knowing surely that Shane Long would make an appearance at some point.
Hoolahan's selection signalled some intent to play the ball around Denmark, but who was going to give the ball to him? A midfield, in its most rudimentary sense, should consist of somebody to win it and somebody give it. O'Neill stripped his midfield bare to frontload the pitch. This was less an example of bringing a knife to a gun fight than it was bringing a one-armed man wildly brandishing a knife to a gun fight.
Christian Eriksen could hardly believe his luck as he was given the freedom of Dublin 4, and he unsurprisingly made hay. This should not necessarily be dressed up as an Eriksen masterclass, Ireland were very hospitable opponents. Ireland's football under Martin O'Neill is often referred to as archaic - Simon Kjaer called it "primitive" - but this proved to be something revolutionary, a kind of postmodern approach to the game; football without positions, without a formation and without a plan.
Jeff Hendrick was briefly Ireland's entire midfield, until he went to centre-back to replace Ciaran Clark, sacrificed for Shane Long. then, it appeared to consist of nobody. Ireland ended the game with six forwards, a midfielder, a pair of full-backs, Shane Duffy and Darren Randolph.
Shay Given's comments on exactly what Martin O'Neill does for Ireland bubbled to the surface ahead of this game, but the peculiar alchemy struck in Cardiff and Copenhagen kept those questions in abeyance, glossed over as Martin O'Neill was portrayed as a kind of genius chemist, finding the right solution regardless of what he had at his disposal. Tonight it blew up in his face however, and he, Roy Keane and the rest of the management side now face a discomfiting few weeks.
Tony O'Donoghue asked James McClean afterward whether this was proof that spirit alone was not enough. Often it is, and perhaps it would have been good enough to beat Denmark tonight had it not been fractured and shattered by a moment of panic by the manager.
Ireland do not have the players to compete at the elite level, but it is extraordinary to say that we do not have the nous to organise them.