The 74-year-old Italian won the acclaim of a nation when he guided the Republic of Ireland to their first major tournament finals for 10 years.
However, inside nine brutal days, he saw the team he had built and schooled to the point where stubborn resistance had become an art form simply fall apart in the heat of battle.
In truth, Ireland were always going to have to punch above their weight to get a great deal out of a group with saw them thrust into competition with Croatia, Spain and Italy, but the Spaniards in particular proved irresistible as they coasted to a 4-0 victory in Gdansk in their second group game.
Trapattoni freely admits he did not expect the capitulation he witnessed in Poland, nor was he initially able to comprehend it.
However, given his time over - and he will get a chance to test the theory in New York during the early hours of Wednesday morning - he believes his team would fare significantly better.
He said: "If we could repeat our Euros without this great weight on our shoulders and without one or two silly mistakes, I think we could repeat this game and not suffer against Spain.
"At that moment, we were a very, very good team and we achieved qualify very well. But after 10 minutes, we conceded a goal against Croatia, and we lost our confidence.
"I would like to repeat this game. Every 90 minutes until that moment, we had trust and confidence because the team achieved qualification."
Trapattoni has since analysed what went wrong during the summer, and admits a relative lack of experience - only Shay Given, Richard Dunne, Damien Duff and Robbie Keane had been to a finals tournament before - had taken its toll.
He said: "After this disappointment, I couldn't understand why the team played well until the Euros, but I know this now.
"It's a different weight, the international game. We qualified for the Euros, but a lot of football is in the head and many of the players did not have this habit in international football.
"At that moment, only people like Robbie Keane and Richard Dunne had experienced this, and there was some anxiety among the players.
"It was important that we started a new attitude, a new mentality. That was our job."
Things were to get worse for Trapattoni before they got better with a 6-1 World Cup qualifier defeat by Germany at the Aviva Stadium in October very nearly costing him his job.
But he survived and a significantly altered team has since lost just one of the eight games it has played.
Ireland have not, however, faced an opponent of the status of Spain, who are preparing for the Confederations Cup, during the intervening period, and the manager is taking a realistic approach to their final fixture of the campaign.
Trapattoni said: "The team is the team of the World Cup - Xavi, (Xabi) Alonso, (David) Villa, (Andres) Iniesta, (Fernando) Torres.
"Sure, they will win, but it will be a good test for us."
Asked where the current Spanish side ranks in terms of great teams of the past, Trapattoni embarked upon a characteristically colourful, if baffling, reply.
He said: "Twenty years ago, a Ferrari travelled at 280km/h; now it is 300km/h. Football changes, players change, systems change."
Just how much the Republic have changed in the last 12 months will become clear on Wednesday morning.