Pep Guardiola refused to blame his tactics or the defence after Manchester City crashed out of the Champions League in Monaco.
Guardiola's decision to field an attacking side at Stade Louis II to build on their 5-3 first-leg advantage did not pay off as City lost 3-1 to go out on away goals.
City were overrun and sloppy at the back as they conceded twice in the first half, while further defensive frailties were exposed by Tiemoue Bakayoko's decisive third goal.
Guardiola had said before the game he felt attack would be the best form of defence but, having left Yaya Toure on the bench, City could not create a midfield platform for their forwards to operate effectively.
Guardiola said: "All managers make mistakes but I don't think it was down to a tactical mistake.
"It's simple. The difference was between the first and the second half. In the second half we tried to win the game, we tried to play. I did it all my career in that way.
"But the problem was the first half. We weren't there. We wanted to show personality, not to let them think, but they could pass and pass the ball. We forgot to do that in the first half.
"My mistake was being not able to convince them to do that. I did in the second half but it was too late."
Guardiola played his attacking big guns of Leroy Sane, David Silva, Kevin De Bruyne and Raheem Sterling with Sergio Aguero up front. He felt it was their failure to get into the game that cost City, not their defensive vulnerabilities.
He said: "No, it's not about the defence. Today was not about that. Why was the second half a problem with the defence? The problem was the first half when we were not there.
"Our strikers have to be aggressive and pick the ball up, but we didn't, at this crucial time. That's why we are out.
"We have to play for more than 45 minutes. It's not about the defence and the goalkeeper."
City's elimination meant for a first time that Guardiola, who twice won the Champions League with Barcelona, had failed to take a side at least as far as the semi-finals.
Hailed as the best coach in the world, Guardiola was recruited in the hope he could steer City to glory in the competiton.
He said: "I came here to win the Champions League? I tried, I tried - and I will try again.
"Playing like we have done this season, like in the second half, would have been enough.
"The competition is so demanding. Hopefully we are going to learn so that, next season, we can come back here and make the same performance we did at the Etihad for the whole 90 minutes."