England manager Martin Johnson admitted the four yellow cards handed out to his side played a key role in the 32-6 defeat by New Zealand at Twickenham.
"The sin-bins didn't help, to have four guys in the one game is pretty unusual," said Johnson.
"There were times where we thought we had their guys under pressure but we didn't make anything of it.
"Maybe our guys have got to learn that Test rugby is about pressure. When you make mistakes they'll kill you."
England gave away a total of 15 penalties in the contest and were hampered by the sin-binnings of Lee Mears, James Haskell, Toby Flood and Tom Rees.
Johnson's team have now lost their last three games, at home to Australia, South Africa and New Zealand, but the two-time British and Irish Lions captain says his young side will be better for the experience.
"I think they're learning the lessons," added Johnson. "At times we made them look average but then it tells in the last 20 minutes - fitness.
"I think a lot of our guys are playing a Test match series for the first time, and it shows.
"We know we've got lots of guys that can play at this level, but we've still got areas where we need to improve as a team, things like composure, the intangibles.
"There were times where we needed to get take a grip on the game and slow it down and we didn't do that and paid for it.
"New Zealand made mistakes but we didn't take advantage and that's the difference in the game.
"But you're not helping yourself obviously when you have 14 men for half the game."
And Johnson said there were positives to be taken from the November series.
"If you lose three on the trot you have some issues," Johnson told BBC Sport. "But we have found some good players this month.
"Delon Armitage has been one of our stand-out players, Riki Flutey has played very well, so has Toby Flood and Danny Care has learned a lot about Test-match rugby.
We did the business and the boys have been superb
New Zealand coach Graham Henry
"We will be a more battle-hardened group. It has been a long four weeks, we have not got the rewards we wanted and frankly we have not deserved to.
"But we are in this as a group and we are looking forward to the Six Nations."
And full-back Delon Armitage, who has impressed with his displays this month, says the players are determined to improve by the time they gather again for next year's Six Nations.
"We are taking the positives out of this series," he told BBC Sport. "We created a lot of chances against the top teams in the world.
"We have to finish off those chances, it is a learning curve but we have to go back and work hard on the little things. In February we will be a different team."
New Zealand coach Graham Henry paid tribute to England, after leading the country to their third 'grand slam', while hinting that refereeing in the Guinness Premiership may have contributed to the home side's high penalty county.
"I thought England played with a huge amount of character. They put a huge amount of pressure on us - there were a lot of youngsters out there who haven't played much international rugby," he said.
Henry delighted with Kiwi victory
"Martin will be happy with the guts and character showed - I think this was a step in the right direction for them.
"You wonder about the refereeing in the Premiership, whether they're strict enough.
"They might be getting away with it in the Premiership, but not with stricter international referees. It's not just something that happened in the last two Saturdays.
"We did the business and the boys have been superb. Winning a 'grand slam' is difficult to do, it's only been done three times now.
"We showed a lot of character in the first half, hung in there and then dominated in the last 20 minutes.
"That proves the backbone of the team. The guys have won all of the trophies available to them this year."
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