Mancini belives that his side's inability to convert chances has ultimately see them come up short in a failed effort to retain the Premier League title.
He told The Mirror: "This is our season, exactly, in 90 minutes. In the first half, we missed three incredible chances. In the second half, another three.
"There are some years that are difficult when you don't score enough goals to win the Premier League. Last year we scored I think 20 more goals by this stage and we are missing 20 and that is too many.
"We can't know which player can score 25 goals next year. But I think we have good players, we were unlucky this year probably. Now it is important we win the FA Cup and after we have time to buy to improve our team."
City are back in Premier League action at home West Bromwich Albion on Tuesday night before next weekend's FA Cup final against Wigan Athletic.