Inter Milan boss Frank de Boer is shocked by his side's performance in Thursday's 2-0 Europa League loss to Hapoel Be'er Sheva at the San Siro.
Goals from Miguel Vitor and Maor Buzaglo eased the Israeli club past the three-time European champions on the night.
And De Boer said he would take a second look at the game to try and determine what went wrong.
"We have to analyse this game. First of all I am very sorry for the fans who came to the stadium, because we didn't win," De Boer told Sky Sport Italia.
"We lost the ball many times too easily and were very sloppy. Eder hit the woodwork and in the second half we had total control, but on a free kick [Jeison] Murillo was out at that moment and they blocked us to create space for the goal.
"Much like at Pescara, we lost our heads a bit after going behind. We started playing well in the last 20 minutes and were confident we could score a goal.
"I don't understand how we can lose our heads like that when we are just 1-0 down and there's time to recover. We should continue working and not lose control like that.
"I am angry because I'm convinced we could've scored the first goal and had the chances to do it. That's the way it went, I am confident we can improve."
Hapoel Be'er Sheva manager Barak Bakhar praised his team's performance, highlighting the level of preparation needed to achieve the result.
"Before the game I said we'd be ready, that we had prepared for this carefully," said Bakhar in a news conference.
"Everything we had planned worked and I am very happy with this fantastic result.
"Were Inter poor on the night? I look at what my own team does. Inter are exceptional, but we did well to make them play badly.
"Inter remain a top level team."
De Boer's men must rebound from Thursday's disappointment quickly as a matchup with arch rivals Juventus looms on Sunday.
And the Dutch manager says belief will be the key against their Italian rival.
"We only didn't play that well in the first 15 minutes, losing the ball too easily, but then we controlled the game," De Boer said. "After the goal for eight minutes we lost our heads, but I am sure if we believe in ourselves, then we can hurt Juventus."
Inter defender Andrea Ranocchia was focused on the future afterward.
"It's a defeat. Unfortunately we hoped for another result, but it's done now, we have to focus on Juve. We are disappointed, but have time to recover and go through," the defender told Sky Sport Italia.