Memories of 2007, when the team failed to progress from a challenging pool, still trouble some members of a squad that O'Callaghan concedes has failed to fulfil its potential.
The Lions second row insists it is crucial Ireland, who open their World Cup against the United States in New Plymouth a week on Sunday, make their presence felt on rugby's greatest stage.
"You don't want to get to the biggest competition of your life and fall flat on your face," he said.
"The scars of France have stayed with us all. It was a scarring event in our careers.
"It was hugely disappointing because you arrive with such promise and all the dreams of doing well. So to come up short....there's no worse feeling.
"It took me a lot of time to get over that and some of us still haven't.
"A lot of us pretend 2007 was a leap year, that nothing actually happened during that year!
"We might as well have taken a year out given the way we played.
"We have a good squad with good players but we haven't done ourselves justice.
"This is the big show, there is nothing bigger than a World Cup. This is the one we've been dreaming of since we were kids.
"There are times in your career when you have to front up. We managed that in the Grand Slam game against Wales in 2009.
"Before people thought Irish teams choke at big events, but beating Wales was the result that over-turned that perception.
"Big games can be the highlight of your career, or the most scarring event."
While Ireland arrived in France four years ago voicing their ambition to reach the semi-finals, their approach to the coming weeks in New Zealand is vastly different.
The official line prevents any player from looking beyond facing the United States in the belief the squad will benefit from a more grounded attitude than the one adopted in 2007.
"If we start looking beyond the first game, which we did four years ago, we'll fall flat on our face. Hopefully we're in a better place now," he said.
"If you look at our track record we've often been disappointing and then maybe been able to put in a massive performance or a few together.
"But the big thing is that we know that now. Now we have to do whatever it takes to win.
"It might be ugly and poor to watch but no one back home would care if we advanced playing that type of rugby. We need to gather momentum and get results."
Adding a sense of urgency to the coming weeks is the realisation that many players - the 32-year-old O'Callaghan possibly among them - are playing their last World Cup.
"In terms of personal drive, there will be a few of us who will be thinking this could be my last shot so I want to empty my bag," he said.
"If everyone gives everything and comes away feeling they couldn't have done any more, it's all you can ask."
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