Liverpool and City were by far the best two teams in the league last season, but as the campaign went on the lead of Jurgen Klopp's side at the top of the table grew and grew.
They eventually won their first top-flight championship in 30 years at a canter, finishing 18 points adrift of City.
City, meanwhile, dropped points in surprising fixtures, most notably losing against Norwich, Wolves twice, and Southampton.
De Bruyne insists the types of mistakes which led to losses in those types of games need to be eradicated.
“A lot of the time this year we played good enough but we didn't capitalise on their mistakes and we made a few too many mistakes.
"Other teams got goals and points out of it and that is the difference. I don't think a lot has changed from previous years but we made too many mistakes and lost too many points."
However, De Bruyne does not think that the 18-point gap between the two sides last season is a reflection of the difference in quality between the teams.
"I don't think the gap is 18 points but it goes so quick. A few years ago Liverpool were so many points behind, then they got closer," he added.
“It can change so quickly, I don't think you can ever base a season on points difference because Liverpool lost a few games but [when] they were champions so you never know what the real distance is between the teams."
Although a well-publicised pursuit of Lionel Messi fell through for City, they have still recruited Ferran Torres from Valencia and Nathan Ake of Bournemouth this summer, while the transfer of Napoli's Kalidou Koulibaly remains a priority.