Arsene Wenger accused his Arsenal side of "repeating the same mistakes" as they were beaten 4-2 by Nottingham Forest in the third round of the FA Cup on Sunday.
Having made nine changes for the clash at the City Ground, the Gunners produced a below-par performance against their Championship hosts.
Forest led 2-1 at half-time and scored two penalties in the second half to condemn Wenger to his first FA Cup third-round defeat.
"I knew before coming here, it would be a tricky place to go," said Wenger afterwards. "You know when you come back it was important not to make a mistake again - that's why it's disappointing because during the game, we repeated the same mistakes and that's where we were guilty today. Once, twice, three times, and at that level, you cannot afford that.
"We were not good enough anywhere, not at the front, not in the middle, not at the back, and we paid for it. They looked sharper, had more chances, and that's all I can say. They had an outstanding performance and I couldn't fault any of their individual performances.
"Overall you can congratulate Nottingham Forest for an outstanding performance - sharp, winning decisive challenges, always dangerous going forward and overall they deserved the win today. Simple as that."
Wenger was watching from the stands as he was serving a touchline ban for comments made about a recent penalty given against Arsenal.
With that in mind, Wenger declined to comment about Forest's penalties, saying: "I said what I had to say many times and I will not talk about the referees. I think I talked about that and that is basically what I think. There is nothing to add."
Asked about the nine changes he made, Wenger added: "We had a very difficult schedule, many players were on the edge and we play again on Wednesday [against Chelsea in the Carabao Cup], it was nearly impossible not to make it [changes].
"I can understand the selection is questioned but it would be an easy excuse, because we have eight or nine experienced international players on the pitch so we played with respect against a Championship side. That would be the wrong excuse.
"It's disappointing we lost, that's all I can say. Some days you have to say Nottingham Forest were better than us and that was the case.
"We have a big game on Wednesday so we have to focus on that now."