Mauricio Pochettino admitted his youthful Chelsea side need to be more mature after their shock 1-0 defeat against Nottingham Forest on Saturday.
Anthony Elanga's goal condemned Pochettino's side to their second loss in the Argentine's four Premier League games in charge.
Former Manchester United winger Elanga punished a mistake from Moises Caicedo, raced onto Taiwo Awoniyi's pass and slotted home in the 48th minute at Stamford Bridge.
Chelsea have won just once in the league this season and are languishing in 11th place.
Pochettino kept faith with the starting lineup that beat Luton 3-0 in the league last week, but his inexperienced team struggled to impose themselves against Forest.
England Under-21 forward Cole Palmer, signed from Manchester City on Friday, was one of several raw substitutes introduced by Pochettino to no avail in the second half, underlining the need for his players to grow more battle-hardened quickly.
"We were not clinical in both areas," Pochettino said. "We made a mistake and then we created opportunities, but if you don't score it is difficult to win games.
"This type of game, I think, will help us to be more mature, it is not only about having quality, it is also about competing in different ways.
"Of course, we can't say that we didn't deserve more, but in football, the stats sometimes reflect what you do and in that case we created but we didn't score and we only had a few shots on target."
LACKING COHESION
Chelsea's owners have spent more than £1 billion on new players since buying the club from Roman Abramovich in 2022, including around £380 million on 10 signings for Pochettino.
At present Chelsea lack cohesion and cutting edge, leaving them prone to punishment if they make a mistake at the back.
West Ham beat the Blues 3-1 despite Chelsea controlling possession for long periods and it was a similar story against Forest.
While it is too early to contemplate Pochettino being under pressure, the former Paris-Saint Germain and Tottenham boss will have noted Graham Potter lasted just seven months before being sacked by co-owner Todd Boehly last season.
Despite their rocky start, Pochettino remains confident Chelsea will turn the tide.
"We are building something and it is always up and down. We are unlucky because I think we deserved more against West Ham and today," he said.
"I have said before, it is only a matter of time."