Tottenham Hotspur boss Mauricio Pochettino thought his team lacked resolve in Tuesday's 2-1 defeat to Leicester City at the King Power Stadium.
A late strike from Harry Kane was not enough to save Spurs after Jamie Vardy and Riyad Mahrez struck for the Foxes in the first half.
"They were more aggressive than us," Pochettino said, with Spurs now 13 points adrift of Premier League leaders Manchester City. "We need to learn and fight from the first minute.
"If you don't fight in the Premier League the quality gap is even. You cannot afford no fight. You cannot win games. If you don't compete in the Premier League you are going to struggle.
"It's difficult to analyse the game. We start so sloppy. The performance in first half disappointed us a lot. First you must compete and fight and be focused and then quality will appear.
"Leicester showed more than us today. Ready to fight in the first half. Even if the game was open and we had chances to score and stay in the game we were poor and this is disappointing and frustrating.
"It's difficult to know why. Not about tactics or systems or selections. It's about the collective. The collective performance was so poor.
"Second half we competed, we fight, and in the end the game finished 2-2 or 2-3 we deserved it. We weren't clinical in front of the goal. We had easy chances to score."
Spurs will need to improve in their next Premier League clash with Watford on Saturday before taking on APOEL in the Champions League next Wednesday.