Arsene Wenger said it was "sad" to see Arsenal's FA Cup run come to an end but urged his team to bounce back by making "the impossible possible" against Barcelona in the Champions League.
Arsenal's quest for a third straight FA Cup ended with a 2-1 quarterfinal loss to Watford at the Emirates on Sunday -- the latest in a string of disappointing recent results.
"Our long run in the FA Cup comes to an end in a very sad way because I didn't think we deserved to lose this game," Wenger said.
"Of course it is sad. But the FA Cup is the FA Cup -- you cannot guarantee that you win it."
Arsenal dominated much of the game but struggled to create clear scoring chances, and Watford capitalised by striking twice in the second half.
Danny Welbeck pulled one back in the 88th minute but also missed Arsenal's best chance of an equaliser, firing wide of the far post in injury time.
But Wenger said: "It's difficult to understand why we didn't score [more].
"I think we had enough chances to win the game. But it was a typical cup game against a team that comes and fights and takes their chances, and us trying to score. There's not a lot more to say."
He also said he did not believe that defender Gabriel should have been sent off for his strong challenge on Watford skipper Troy Deeney, adding: "It did not look it to me [that he should have been]. He won the ball, and it looked to me that Deeney also did [have both feet off the ground].
"Both players went for the ball and Gabriel got there first, that is how it looked. Maybe if both feet were off the ground, I will have to look at it again."
The FA Cup had been seen as Arsenal's best chance of a trophy this season, with the Gunners needing to overturn a 2-0 deficit against Barcelona at the Camp Nou on Wednesday in the Champions League and eight points behind Premier League leaders Leicester.
But Wenger said: "Look, when we win it you say it's only the FA Cup, so you cannot say on the other hand that it's a disaster [to lose].
"We had enough technical superiority to win the game and score goals. It was down to not making a mistake and keeping it 0-0 until the last 20 minutes, when we could have won the game. Unfortunately, we made one."
While Wenger fielded a strong lineup, with Mesut Ozil and Alexis Sanchez starting, he said he wdid not plan to rest players in Barcelona in order to prioritise the Premier League.
"No, no, no, we want to make the impossible possible," he added. "We know we are playing against a very strong side, and it's important that we go there and focus and show a very good response.
"I think this team has a great spirit, a very strong attitude. They play at the moment with the idea that they cannot afford any [bad] result, but we can deal with that. "We have a good opportunity to show on Wednesday night that we are up for it."