He said: "They had 22 very strong players. We put a lot of effort and passion into the game but lacked discipline.
"We made too many personal errors and when you make a mistake against a team like England you pay for it.
"We tried and came close to scoring a try, but it was not to be."
Italy coach John Kirwan fielded a particularly youthful line-up, and De Rossi accepted that the team's lack of big-match know-how had proved their undoing.
"Some of our younger players have never played in a stadium with 25,000 people, and we lacked experience at times," he said.
"Now we have to focus on next Saturday's game [against France at the Stade de France] and hope that it will be a different story."