Jose Mourinho admitted his young Chelsea team lack the maturity to cope with difficult situations after his return to the Champions League started with a shock 2-1 defeat against FC Basel.
Mourinho's first Champions League match as Chelsea boss for six years proved a dispiriting experience as the Swiss side came from behind to hand the Blues their first home loss in the group stage of Europe's elite club competition since 2003.
Brazilian midfielder Oscar had given Chelsea the lead just before half-time at Stamford Bridge.
But a sloppy display was punished as Mohamed Salah equalised after the break and Marco Streller bagged the winner with nine minutes left.
Just 24 hours earlier, Mourinho, whose previous spell with the club ended with the sack in 2007, had asked for patience as he builds a new-look Chelsea, claiming he needed time for his young players to grow up.
And Chelsea's second successive defeat, hot on the heels of a 1-0 loss at Everton on Saturday, left Mourinho conceding his youthful team were too inexperienced to know how to react when the momentum swung against them.
"I think this team probably is not a team with such maturity and personality to face the difficult moments in the game," he said.
"Against Everton we played amazingly and yet when they scored you could feel the team was struggling despite dominating and today was a bit the same.
"We were pressing and trying to be creative but when the most negative moment arrives the team shakes a little bit.
"We go home sad but we have to work hard, it is the only way I know. We have to believe in each other, be critical inside to try to resolve things, but stick together and try to get a result against Fulham on Saturday to put a smile back on our faces."
Last season, Chelsea became the first Champions League holders to fail to qualify for the last 16 in their defence of the crown, yet even that dismal European campaign, which began with a draw against Juventus, didn't start as badly as this one.
But Mourinho will surely get Chelsea back on track as he learns how to get the best from raw recruits Oscar, Eden Hazard and Marco van Ginkel, and he is confident the defeat will not damage their bid to qualify for the knock-out stages.
"We must get these three points somewhere else, at Basel, Schalke or [Steaua] Bucharest to make sure we reach our objective of finishing in the top two," he said. "It is not lost yet of course. I will fight for it and I believe very much we will achieve it."
Chelsea's cause wasn't helped by lacklustre displays from Cameroon striker Samuel Eto'o and Brazil forward Willian, who was making his debut after a £30 million (HK$371.11 million) move from Anzhi Makhachkala.