The English giants suffered a poor first season under the Portuguese manager and made a faltering start to the current campaign before winning three games in a row.
United then salvaged late points in a pair of 2-2 draws with Nottingham Forest and Tottenham after blowing leads in both games, with a failure to close out those games compounded by Monday's 1-0 loss at home to 10-man Everton.
That defeat has added to the pressure on United ahead of Sunday's Premier League match away to a Crystal Palace side who started the weekend sixth in the table, four places above Amorim's men.
"In our club, it's the same thing because last year we had to win every game all the time," Amorim said when it was put to him that this was the kind of match United should be winning.
"We took a lot of things, a lot of criticism because we were not winning, so in our club, there are no excuses.
"I said the same thing last year when we were in Europe, and I said the same thing this year, the advantage and the disadvantage of not being in Europe, so there are no excuses. Last year or this year, we have always had to win games."
Amorim, asked if he was disappointed by United's 10th place in the table, replied: "I think if I look at the games, we should have more points because we had control of some games, we had the advantage in some games, and we lost that control.
"So, if I look at our games, we should have more points, and that is really disappointing and really frustrating, especially the last game."
Matheus Cunha, Benjamin Sesko and Harry Maguire remain absent for Sunday's match in London.
Palace have made huge strides under Oliver Glasner, who led the club to a historic FA Cup triumph in May and has previously faced Amorim with Eintracht Frankfurt in the Champions League.
"I played against him in Frankfurt with Sporting, so I know the (style of) play," said Amorim.
"I take inspiration from everyone. When I have two weeks for (an international break), I watch all the managers and try to take all the inspiration that I can.
"I have six years as a professional manager, so I'm always trying to learn to improve my team."