Everton boss Marco Silva felt his players had been "too nervous and anxious" during the 1-0 New Year's Day loss to Leicester at Goodison Park.
In a contest that was low on quality and entertainment, the Toffees registered only two efforts on target, with the first not coming until the 75th minute.
Jamie Vardy struck the winner in the 58th as the Foxes punished a mistake by Michael Keane.
Silva, whose men have lost four of their last five matches, said: "It's a disappointing result for us and a poor performance also. It wasn't a good game to watch.
"We missed some of the most important things in football, to pass the normal pass and to do the easy things. We missed many, many times.
"The first half, even when we were in control of the game, when we won some balls, afterwards our decision wasn't the best.
"I felt our team was too nervous and anxious, without reason.
"When you play in this way with easy mistakes, the bad things come to you and that is what happened with the goal we conceded.
"After that, if you were nervous and anxious, you will be more, for sure. After, we didn't play with enough quality to create the chance to change the score.
"I told them what I am telling you. When you didn't achieve, you have to react and we have the quality to react and play better than what we did this afternoon."
Everton, 10th in the Premier League, have won only once in eight games.
Silva said: "We played four games in 10 days, it is really tough, even if you change players. It is not easy to see the players fresh with high mobility every time.
"And when you play against these type of teams, that come here and are waiting for your mistake, you have to put high intensity and mobility in your game.
"But it is not reason to (play as they did). We are playing at home, our fans were, until a certain moment, behind us, pushing our team to win, and I cannot find – but I will find, for sure – the reasons to (play like) that."
Silva was asked if he was worried about his players' mental strength, and said: "I understand your question, but you are working in Everton, it is a big club and there is pressure to win matches, to react.
"To be here, play at this level, work at this club, you have to show the capacity to handle this type of normal pressure."
Leicester, who rose a position to seventh, have won three out of four, with the other victories coming against Chelsea and Manchester City. The other match was Saturday's 1-0 home loss to Cardiff.
Boss Claude Puel has been ranked among the favourites with bookmakers to be the next manager in the division to leave his post, and a report on New Year's Eve linked Newcastle's Rafael Benitez with Leicester.
Puel said: "I don't like to make bets, for my part. I am not sure how that works, putting a bet on. That is not my concern. The most important thing is to show our quality.
"I will defend my team, my squad and the club, and I am just a person who serves the club, that's all, and I would like to continue this way. Speculation – I cannot have an impact about this.
"I cannot have an opinion about people outside the club. About our fans, the squad, the club, the directors, staff, it is always the same way, with stability, without problem. I cannot manage the rumours. There is speculation, I don't know why, but it is not my concern."