Ten Hag said: "The attitude, it starts always with the right attitude during the week and on matchday you have to be spot on.
"When we missing seven starting 11 potential players we are still competitive with one of the best teams in the league.
"When you don't have the right attitude to find the moments to press or you don't make the recovery's then you make it very simple for every opponent."
On Casemiro's error for the goal, he said: In that situation he is a midfielder playing in that position and making a small mistake, but it has hard consequences.
"I think for United players every game is a final and you have to perform and win every game - we should realise this."
On the fans, Ten Hag added: They understand where we are and where this club is. We have so many injuries in key areas they (fans) don't get what deserve, but they understand this and that is why they are behind the team.
I think that is why they are with us we are united and hopefully we can pay them back in the future.
"I have no doubt about this.
"As human beings and my experience that will always happen once in three months when you are not in the right attitude.
"But, mostly this team has the right spirit and they execute the rules and principles of the game even if they have to adapt in their positions.
I can only be happy and it is a big compliment for this team that they executed all that they could and they were fighting."