Joachim Low believes Germany must "raise their game" if they want to get past Algeria in the 2014 World Cup round of 16.
The Germany coach insists his side will have to improve if they want to make it through to the quarterfinals.
"Personally, I cannot remember a group stage in which so many of the favourites were knocked out," he said at a news conference.
"But tournaments are marathons, not a 100-metre sprint. Many nations in the past have won their first three games, and then lost their fourth.
"We've seen it all before. A team's got to be able to raise their game all the time. If you can manage that, then that's a masterstroke.
"There's been lots of light, but also plenty of shadows; some good things, but also things which didn't work.
"We won our group, which was our primary objective, so we are happy, but we are also self-critical and we know that we can play better.
"We've not reached our limit yet, and now the knockout phase begins, the decisive games are here."
Low has taken time to scout Algeria and has been impressed by what he has seen from the North Africans.
"If anybody thinks or believes -- and I think this is a feeling among the general public -- that Algeria are easy opponents and that we can already start thinking of the next round, then they're making a huge mistake," Low warned.
"We must remain focused and on our toes because any complacency will be punished.
"I took a look at Algeria yesterday for an hour and I know we're up against a very compact side who run a lot and are aggressive.
"I've rarely seen a team defend so vehemently, but still attack with purpose. Their whole country is euphoric, so we're up against a strong opponents."
Low completely dismissed any notion that Algeria will have a score to settle with Germany after they were eliminated from the 1982 World Cup as the result of a 1-0 win for Germany against Austria.
"When I hear people talking about revenge, it irritates me," he said. "Apart from maybe [Miroslav] Klose or [Roman] Weidenfeller, none of our players were even born then so they have no idea what happened.
"For our players, it's not an issue."
Low said that Arsenal forward Lukas Podolski will not feature on Monday due to a muscular problem, but that he would be available for selection again "for our next game -- should we get through."
Jerome Boateng also only took part in light training, but he will be available, Low said.
Information from the Press Association was used in this report.