Marco Silva could not understand why Everton turned in a "nervous" performance as they lost 1-0 at home to Leicester City on New Year's Day.
Everton have now won just one of their last eight games after Jamie Vardy struck a second-half winner at Goodison Park following Michael Keane's error, but Silva offered no excuse for his side's display.
Bemoaning the nature of the defeat, the Everton boss promised to look into the reasons for a scrappy performance in which they made mistakes at the back and lacked fluency in attack.
"It's a disappointing result and a poor performance, to be honest," he told Sky Sports. "This is the moment for us, like always, to be honest.
"From the first minute [it was clear] - and we knew before the match - what [Leicester] came here to do. It is easy to understand. They started the game 4-5-1, blocking the space, waiting for our mistake.
"In the first half, we were in control. But every time we were on the ball, we were too nervous - without a reason for that. I felt our team was playing with big issues and without ambition and we were too nervous in some moments.
"Every time we tried to organise or start an attack, we lost [the ball]. The game was a bit confused. We didn't put our game there.
"When you play with so many issues in the game and you're nervous, after come the easy mistakes - like we made with the goal we conceded on the counter-attack with Vardy. It was a normal ball, normal to control [for Keane].
"But we were not under the normal pressure of a football game. We will find the reasons for that."
He added of the team's nervousness: "I told them, 'There is not a reason'. There is no reason for that. If you look at our last results, we have not been consistent, of course, but there is no reason to be so anxious and so nervous."
Vardy was largely anonymous before pouncing on Keane's error, but he insists he never doubted himself when bearing down on Jordan Pickford's goal.
"I don't think you can have any doubts," he said. "Obviously, as a striker, you want to be putting every single effort into the net.
"To be in that position, it shows I'm making the right runs. [Ricardo Pereira] has played a great throughball and I've found the bottom corner."