Brendan Rodgers feels Celtic's 7-1 humiliating loss to Borussia Dortmund was a perfect example of how brutal Champions League football can be at times.
Celtic were riding high after their opening Champions League match last month when they defeated Slovan Bratislava 5-1.
But they were quickly brought back down to earth with a bang away to Dortmund on Tuesday night.
Karim Adeyemi bagged a first-half hat-trick with Emre Can and Serhou Guirassy also scoring before the break.
Brendan Rodgers had a night to forget as Celtic manager
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Daizen Maeda momentarily brought Celtic level after the ninth minute, but that proved to be a fleeting moment of respite for the visitors.
Dortmund took their foot off the gas in the second half, but still added two more goals to add to Celtic's misery.
The sobering defeat has left Celtic 19th in the table with six games remaining but could drop out of the top-24 by the end of the week.
Rodgers suggested Celtic were unfortunate to concede as many as they did on the night.
"We are really disappointed with the result and performance," he said on TNT Sports.
"I don't think I've been involved in a game where every mistake we made got punished. That's the level. We could've been better with the ball.
"Going down early spooked us a little bit and we didn't play with the same confidence.
"Second half, the guys showed great spirit and we had more possession of the ball, took more risks to create. Ultimately, we were beaten by the better team.
"We will always assess it and look back. We wanted to press but we wanted to be in balance, be tight and compact.
Celtic were thumped 7-1 away from home
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"But there were too many times we ran out at the wrong moment and time. We were not in a compact shape, and top players punish you.
"We needed to have longer spells with the ball, we were too rushed. We were looking for that killer pass too early and constantly giving the ball away."
Neil Lennon was on commentary for the match and suggested after Dortmund's third goal that Celtic needed to shut up shop and play for pride.
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But Rodgers' side continued to leave gaps behind them and try to play out from the back, which cost them dearly.
The Celtic boss was asked whether he would 'adapt' his playing style when playing against some of Europe's elite.
He replied: "We always have to adapt but sometimes the quality just breaks through that.
"Will we camp in and just wait? No, we won't do that. We know it'll be difficult at times. Tonight, we just gave it away too easy and we got punished."
