United were beaten at home 3-2 by Brighton on Sunday.
Amorim said: "It was similar to other games, we suffered some goals that we shouldn't suffer. Then it's hard to have possession because we are anxious.
"We scored the equaliser but the second half was the same thing. When we suffer goals like that then it's hard to turn around.
"We have to understand the moment but understand it's not acceptable for Manchester United to lose this many Premier League games. I don't know why.
"We need to be better, that is really clear, It doesn't matter if we have a lot of time to train or if I know the players, it's not acceptable. We continue to work to change details that change the game."
He also said: "I'm not going to change how I see the game, I'm clear on that.
"The players are going to suffer, the fans are going to suffer, I'm sorry. I have one way of doing things but we need to survive this moment. It's very clear for everybody what we are going to do."