Mauricio Pochettino conceded Tottenham were complacent against London rivals West Ham after surrendering a two-goal lead as they sensationally bowed out of the EFL Cup.
Spurs were in cruise control at Wembley, leading 2-0 after 45 minutes thanks to Moussa Sissoko and Dele Alli as the quarter-finals of the competition loomed on Wednesday.
However, West Ham completed a second-half comeback as Andre Ayew scored twice in five minutes before Angelo Ogbonna sealed the fightback in the 70th minute.
Spurs manager Pochettino lamented the attitude of his players following the break though he acknowledged blockbuster clashes against Real Madrid and Liverpool may have caught up with Tottenham.
"Everyone can see the game," Pochettino told Sky Sports. "The first half was easy, we scored two goals and the game looked over.
"In the second half there was a lack aggression, the game was completely different and we conceded three goals in 15 minutes.
"That was the problem, it can happen in 90 minutes and when you are not on the same mental level, it's difficult because you can concede one goal.
"Then, when the opponent has nothing to lose, they start to believe and then you concede again and suffer.
"That is not good, it's a bad feeling. It's true that it's a different competition. It's bad to lose, I'm not happy and the players are disappointed. It's not a good feeling when you lose."
Pochettino added: "In the second half we should have approached the game like it was 0-0, but the second half was different. We conceded the way that is difficult to accept.
"We have to keep going. We have to understand that after Real Madrid and Liverpool it's difficult to keep the motivation, it's difficult to keep the energy.
"When you play a team who have a lot of quality but are down and receiving a lot of criticism, to give them the opportunity to come alive is disappointing.
"You have to be more mature when you're 2-0 up."