He added: "South Africa wasn't good but we did not play at the same level that we played in qualification. When you play a World Cup competition, you have to arrive in really good physical condition.
"Another thing really important thing is the mind of the players. We played not with confidence but with fear."
Asked if he thought he was a better manager following the tournament, Capello added: "Every experience is important for the players, the manager - I learned a lot.
"When you lose something, the experience is very important, you have to understand what really happened and understand if I, or we, made mistakes and, from that, improve. Everyone makes mistakes."
Capello added that he had received three job offers since England were knocked out in South Africa. "They were from important clubs but I don't want to speak about them because I respect the managers who are working there now," he said.
He also played down reports of a communication problem with the England squad after Paul Robinson and Wes Brown both retired from international football at the weekend.
The Blackburn goalkeeper and Manchester United defender made their decisions after being called up for Wednesday's friendly at Wembley.
Capello said: "I accept the decisions. Robinson called us and said he wanted to stay at home. I spoke with Brown here. I told him why I didn't select him for the World Cup because he didn't play for the last two months [of last season].
"This time I selected him because he played all the pre-season games but he said, 'thank you, but I've decided I prefer to stay at home'.
"You have to accept what they want to do. I think it's an honour to be with the national team and to play for England."
Asked if he was concerned about the lack of first-team opportunities for young English players in the Premier League, Capello said: "Players need to play to be monitored during the season - I can't select players who don't play.
"It's not my problem, I select the players - that's the problem of the teams and the players."
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