O'Callaghan, a Lions tourist in 2005 and 2009, was part of the Ireland side that crashed out of the last World Cup at the group stages and ranks the failure as the worst feeling of his rugby career.
"It took me a lot of time to get over and some of us still haven't," said O'Callaghan.
"This is the big show, there is nothing bigger than a World Cup.
"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."
Ireland enter the showpiece tournament under pressure following a frustrating warm-up series where Declan Kidney's men lost all four of their matches.
But the Munster giant is confident Ireland have the mental toughness to bounce back at the prestigious competition.
"There are times in your career when you have to front up," said O'Callaghan.
"We managed that in the Grand Slam in 2009. Before people thought Irish teams choke at big events, but beating Wales was the result that over-turned that perception."
Ireland begin their quest for global supremacy against the USA on September 11, and O'Callaghan is targetting a winning start in what is likely to be his final World Cup.
"If we start looking beyond the first game we will flat on our face," added O'Callaghan.
"Hopefully we are in a better place now. 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."