Brian O'Driscoll did not foresee Ireland's shock defeat to Japan in their second game of the World Cup on Saturday.
Joe Schmidt's side were defeated 19-12 by the host nation, picking up a solitary bonus point from a game for which they had been strong favourites to win.
"The mood of the whole country has just shifted in 80 minutes," said O'Driscoll on ITV's coverage of the game.
For one, I didn't seen that happening. I knew it would be a tough game, playing against the host nation - they have nothing to lose.
Huge credit to Japan, they played terrific rugby.
Ireland looked very blunt. They looked devoid of ideas, they looked devoid of energy actually. I wonder did the conditions and the humidity take effect because it wasn't the Ireland we've come to expect over the course of the last couple of years.
It's very disappointing. It's not the end of the tournament. They can still top the pool, but they have some amount of work-on if they're even thinking about getting beyond the quarter-final.
Paul O'Connell was also an analyst for ITV on Saturday.
"They looked very flat," said O'Connell.
"They replaced the two props after 45 minutes. We thought [Iain] Henderson looked quite flat in the second half.
"A big thing for Ireland over the last couple of years has been their ruck. They've had the best ruck in the world, in terms of ball retention and in terms of speed of ball. And Japan has just absolutely done a job on them at the breakdown.
"Japan's breakdown was absolutely phenomenal. I think they only gave away one penalty, maybe two with one late on. Ireland gave away six penalties at the breakdown, but that's only half the story.
"Every time Ireland had possession, Japan were managing to get one, two hands on the ball. Every time they were slowing it down so Ireland couldn't secure fast ball when they had it.
"I think that's the real story of the day. The way the Japanese played, the way they held onto the ball, they tired Ireland out and their ruck was just phenomenal."
O'Connell added that the Japanese performance was "polished in every way".
"Ireland went to the maul in their first two lineouts and we commented here how excellent the Japanese maul defence was, how tidy it was - Ireland didn't budge them an inch.
"We thought there might have been an advantage for Ireland at the scrum - it didn't come, Ireland might have got one scrum penalty, Japan might have got one scrum penalty."