Martin Johnson slammed England's lack of discipline after their 14-13 defeat to Ireland at Croke Park.
England conceded 18 penalties and had Phil Vickery and Danny Care sin-binned, taking their yellow card tally to 10 in four matches.
Johnson said Care's dismissal for a mindless barge on Ireland prop Marcus Horan with 11 minutes remaining had cost England the chance of victory.
At the time Ireland led 11-5 courtesy of try and drop-goal from Brian O'Driscoll but Ronan O'Gara converted the penalty to push his side two scores clear.
England staged a late rally and Delon Armitage scored with two minutes left - but it was too late.
"I thought we handled them defensively pretty well in the first half but the penalties weren't great by half-time and it got worse," said Johnson.
"I said to the players after the game, you cost yourselves the game. Face facts, it was a big effort, they did some things very well at times but if you give away 18 penalties you are going to lose.
"The one that really changed the game was Danny's. It was 11-6, it made it 14-6 and we had no scrum-half for 10 minutes.
"The focus this week has been not giving penalties away and trusting our defence and being accurate in that area - and they have done it again.
"I am angry for them, not me. We have gone toe to toe with one of the better teams in Europe, a team that could win this championship.
"We were under pressure at times and at times we had them under pressure - but if you give 18 penalties away you are not going to win."
Johnson said it was too early to decide whether any players would pay for the indiscipline with their place in the side.
"It is not the same people but we will be talking about it for two weeks (before playing France)," he said.
Johnson was pleased with the way England coped to being down to 14 men for 20 minutes and feels his side are improving.
But over the next fortnight, Johnson will continue to hammer home the message that his players must trust their defence and not concede penalties.
"These are in big passionate one-off games here. We were playing in a volatile, passionate place and despite the penalties we kept ourselves in game very well and we handled what they had to throw at us attacking wide," he said.
"That makes it all the more frustrating. We didn't need to give penalties away because we weren't getting broken in defence.
"Two weeks ago against Wales I thought we had a chance to win. This week we certainly did.
"They have to understand they have cost themselves a Test match. We have conceded one try way from home again. The defence is good, we have got to trust it."
England Under-18 head coach John Fletcher insists his young side will be better for the experience after beating Italy in the bronze final to round out their 2015 Rugby Europe U18 Championship campaign in style.