Pep Guardiola admitted on Tuesday that he still feels responsible for the manner of Manchester City's Champions League exit last season, saying they have to "close these gaps" as they chase European glory.
City, who host Porto in their opening group match on Wednesday, have never gone beyond the semi-finals of the competition despite all their domestic success in recent years.
Memories of the quarter-final loss to Lyon in August remain fresh for Guardiola, who won the competition for the second time as Barcelona boss in 2011 but has failed to lift the trophy since.
"It was a tough moment," said the Catalan. "I felt so responsible for how the club felt, the players. I was not able to drive the club and I feel responsible.
"But watching the games we have to accept the reality that we were not good enough. We did not play bad, we played some real good moments but we sometimes made mistakes and in this competition you cannot do it."
Guardiola said City were not far away from cracking the secret of European success.
"I always had the feeling we were close," he said. "The gaps were little but you have to close these gaps. We have to solve it.
"It's the past. Now is a new opportunity and we are going to start at zero again."
The former Barcelona and Bayern Munich coach said Wednesday's fixture had added significance because it was at home.
"The reality to win the home games is so important for qualification," he said. "We're still a little bit away from where we want to be."
City were without Kevin De Bruyne, Gabriel Jesus, Aymeric Laporte and Benjamin Mendy for Saturday's 1-0 win against Arsenal, but Guardiola said the situation was slowly improving.
"Oleksandr Zinchenko is back and other players are back," he said. "Ilkay Gundogan, Bernardo Silva and Joao Cancelo are in good condition. We expect Benjamin Mendy back soon so the team will grow."