City have the chance to end the season with a trophy as they prepare to face Crystal Palace in the FA Cup final.
But Haaland concedes this season hasn't been good enough from City.
He told BBC Sport: "We haven't been stable enough this season and we haven't won enough games, it is as simple as that.
"We have to perform better in the big games. We haven't won enough consecutive games.
"Of course, we have had injuries throughout the season. But we should not search for excuses.
"Every single one of us hasn't been good enough and we haven't been at our best, so when you are not at your best you aren't going to win games in this country because it's so hard."
A horrific season
However, Haaland admits winning the Cup would offer some hope for next season.
He also said: "This season has been tough. It is not nice to lose so many games, it is boring and not fun. That's why we need to finish well and get a trophy.
"It is a good habit to reach Wembley and always important to win trophies. We have the FA Cup final to play for and in a horrific season we still managed to do this, that says it all.
"When you have won four league titles in a row, if you don't win five it's not going to be a successful season. Those are the standards we have set. We haven't done good enough in the league but still hoping for Champions League qualification.
"Crystal Palace are a really difficult club to play against. At Selhurst Park we drew (2-2 in December) and they started really well at the Etihad (in City's 5-2 win last month). They are an amazing team with quality players."