Pep Guardiola's biggest regret this season has been a failure to rectify Manchester City's problems in defence and attack - something he noticed in the Champions League thrashing of Steaua Bucharest.
A 2-1 defeat to Chelsea at Stamford Bridge on Wednesday stretched City's run without a win in all competitions to four games, leaving them 14 points behind the Premier League leaders with eight games remaining.
The result underlined what has been a mixed first season at the Etihad Stadium for Guardiola, with City enduring a meek title challenge and a European exit at the hands of Monaco but remaining in the hunt for a top-four finish and FA Cup triumph.
Guardiola has vowed to improve in 2017-18 but admits he is hugely frustrated that he failed to act on concerns he spotted in the 6-0 aggregate win over Steaua in the Champions League play-off round.
"I will be better, definitely. It was a lesson for me this season," he said ahead of City's clash with Hull City on Saturday.
"It is normal when you are a manager for eight or nine years to have a season where you are not as successful as before, that can happen. You learn about that.
"The only regret that I have myself is that knowing our problem was in the boxes [and] I was not able to solve it. [I noticed it] in the first game in the Champions League against Steaua Bucharest. We won 6-0 but normally it would be 12-0, that game.
"We missed two penalties and an amount of chances. We said 'wow' and were so happy because the first target is to qualify.
"After that in the Everton game, Middlesbrough and these type of games. I realised, okay, we have to play real, real good to win the games.
"When that happened we didn't win by three or four, just one or two. We created chances but had problems to score. After that we suffered at the back. They shoot two or three times on our goal and they score two goals. We have to work harder and harder and better and better to minimise these kind of things.
"The way we played, especially in the big games, we were good but we were not good enough. We have to be honest with ourselves. We were not good enough to compete for the Premier League.
"But it's part of our growth. I never came in as a manager, either at Barcelona, Bayern Munich or when I arrived here, thinking I know absolutely everything.
"Still we have a lot of beautiful things to fight for – to qualify for the Champions League is so important and would be a huge success, and we have the semi-finals of the FA Cup."
City have been without forward Gabriel Jesus since February after the Brazilian fractured a metatarsal, but Guardiola has pointed to a more surprising long-term absentee as a key factor in what he considers a lack of goals.
"The most important thing for [Ilkay] Gundogan is to recover well – it is not easy after six months out with the knee injury," he said of the midfielder, who suffered a torn knee ligament in December.
"He is a player who has a sense of the goal, arriving in the right tempo in the box. We saw against Barcelona, we saw in many games when he played.
"So I like to use him a little bit more for the last pass, arriving to the box, because there he is a fantastic player.
"In [Borussia] Dortmund with Jurgen Klopp and Thomas Tuchel he played in a two, but always as a guy who has the ability to arrive in those positions – he is good with the headers, he is good with the last pass.
"We missed a little bit Gundogan's goals in this part of the season, definitely."
Guardiola also reiterated his belief that City have been affected by controversial referee decisions this season.
"The mistakes are not just against us, the mistakes are against everybody," said the former Barca boss, who called for a summit with referee chief Mike Riley following the 1-1 draw with Liverpool last month.
"Everybody makes mistakes – me, the players and the troupe for Mike Riley. Everybody makes mistakes. But, wow, it [decisions against City] happened a lot."