The Manchester City manager says he identified a problem with his back-to-back title winners as early as the second game of the season against Tottenham – but was unable to solve it.
Defeat to Southampton on Sunday was City’s ninth in a tame defence of their crown, which has seen them drop 23 points behind Jurgen Klopp’s champions.
Guardiola says his side’s failure to capitalise on their dominance over Southampton has been a weakness all season.
“Our consistency (has been missing),” he said. “Not converting our game-plan or the way we played into results.
“The idea is good, but the business is you have to win. When you lost eight or nine games you cannot win the Premier League. Maybe years ago, but not when the champions get over 90 points.
“I was not able to solve this problem that we had since the beginning. I remember the game against Tottenham at home. They made two shots on target and we made more than 20 and we draw.
“It happened the second game in the league and the last one at Southampton was quite similar. I was not able to change this dynamic.”
The defeat to Southampton underlined City’s inconsistency this season – coming just days after beating Liverpool 4-0.
Guardiola has warned his players they must improve if they are to triumph in the Champions League and DA Cup.
“The commitment of the players is without a doubt still after two or three successful seasons unbelievable,” he added. “But we are at the point where we sometimes make mistakes. We have to avoid it.
“In some cases, the lack of scoring goals, they punish us as a team. The semi-final against Arsenal and the game against Madrid is the reality for our team this season.
“If we can play like we play and we are consistent in both boxes, we will have a big chance to go through to the final of the FA Cup and the quarter final of the Champions League.
"But if it happens like against Southampton, Tottenham at home and away and Norwich away, we will be out and Arsenal will be in the final and Madrid will go through.
“This is the reality we have to accept. We have to be lucky to convert what we produce and defend, but I don’t have any doubts the team will be there.”