James Maddison struck in the first-half as Spurs won 1-0.
De Ligt said, "If you lose it's never enough. We can speak about the personal problems, the injuries, but Tottenham have the same problems. If you lose, it is never enough.
"We played OK and created some chances. But if you lose 1-0, you didn't score and conceded one, so we needed to improve at both ends.
"I think the urgency, the hunger to score, that is something that may be lacking. That's not only on the attackers, it's also on the midfield and the defenders. It's a team thing and we definitely need to improve.
"I think you can say (confidence) has taken a real hit. Especially in the Premier League, if you lose the confidence you lose the game.
"We still had a starting XI with first-team players. It's no excuse. It's not nice when you lose five players in one week, but that's part of football, part of life.
"I believe you have to deserve fortune. At the moment, apparently we don't deserve it. I don't believe in fortune coming out of nowhere."