Captain Harry Maguire accepts Manchester United will continue to fall short in their quest for success unless they learn from the mistakes that saw their Champions League hopes go up in smoke at RB Leipzig.
Having fought to seal their return to European football's table and made such an eye-catching start to Group H, Ole Gunnar Solskjaer's side stalled when a point would have been enough to progress.
Europa League football now awaits United in the new year after Tuesday night's 3-2 defeat at Leipzig, who reached last year's Champions League semi-finals but were also thrashed 5-0 at Old Trafford just six weeks ago.
Solskjaer's team went close to snatching the last-gasp draw they needed, but ultimately their passive start cost them as Manchester City loanee Angelino and Amadou Haidara scored in a shocking opening for the visitors.
"We've got to go home, look at ourselves because it's not good enough for this club to go out in a group in the Champions League," Maguire said. "We're disappointed.
"Of course it's frustrating (conceding early goals). As a defender you want to be keeping clean sheets and we seem to be shooting ourselves in the foot in the first five minutes of the game.
"It's a poor goal to give away. We've come here, we've known a (draw) is good enough to get through to the knockout stage and we concede after two minutes. It's not acceptable.
"We've got to look at ourselves. I said it on Saturday (after coming back to win 3-1 at West Ham) and I keep saying it to the lads that we can't keep giving these goals away and coming from behind.
"Although we do have great belief that we can get back into the game, one time we won't manage to do so and unfortunately it's been (on Tuesday night) because we can't start a game like we have done."
Maguire knew the third goal of the evening was going to be crucial in Leipzig and substitute Justin Kluivert grabbed it, moments after Bruno Fernandes' free-kick had hit the bar at the other end.
The Portuguese's spot-kick and Paul Pogba's deflected header led to a nervy conclusion for the hosts, but United fell short in a group that had started with a 2-1 win at Paris St Germain and five-star display against Leipzig.
Solskjaer and his side have plenty to mull over following their premature exit from the Champions League, which the manager believes was down to the shock defeat at Istanbul Basaksehir.
"It has a part to play," Maguire said of last month's 2-1 loss in Turkey.
"We've dropped three points there but I think you've seen the other night against PSG, the amount of chances that we had. We deserved to get something from that game (3-1 defeat at Old Trafford last Wednesday).
"Then (on Tuesday), on another day we create enough to get something from the game.
"But, like I said, we started the game really poor, especially when we're coming away from home at a team that has got a great record at home and we give them a goal after two minutes.
"It's not acceptable and we've got to learn from it and we've got to learn from it quick because if we want to be successful at this club and start winning trophies and start challenging for the best titles we've got to do better."
United will certainly have to do better on Saturday evening when rivals Manchester City arrive at Old Trafford.
"It's the perfect game to have," Maguire told MUTV. "I haven't thought about it as I'm digesting this.
"All the boys are all so disappointed but I've got to pick them up, the gaffer has got to pick them up.
"It's a massive game and there's no better feeling than winning the Manchester derby at Old Trafford.
"At the moment we're disappointed but (on Wednesday) we've got to switch off and recover, make sure we rest and then come Thursday we prepare.
"We prepare for a big game and we need to give our fans something to cheer about."
