The Portuguese star admitted that Pep Guardiola's men, who are 22 points adrift of the table toppers, stopped believing they would retain their crown a month ago.
And Silva, despite Liverpool's sensational form, rues the fact that City didn't push their rivals as far as possible.
He told Sky Sports: "I think we got to a point one month ago where we gave up a bit too soon and that's why we're twenty-something points behind now. We shouldn't have done that and it was not on purpose.
"It was in our head, everyone was disappointed to be already ten or 15 points behind and our heads went a bit down. It's difficult because we're a team used to winning and last season we won everything in England.
"It hurts a lot because when you start a new season you always want to go for the Premier League."