Stuart Lancaster admitted the biggest disappointment of England's defeat to Wales was their loss of composure in the final quarter.
England captain Chris Robshaw said immediately after the game that his side had "unravelled" as Wales stormed to a record 30-3 victory to win the RBS 6 Nations title.
Forty-eight hours on, Lancaster's frustration at the performance of referee Steve Walsh was still clear but it was the reaction of his own team which disappointed him the most.
"When we made the transition from the 2011 World Cup squad through to where we are now, we wanted to find out more about the players and we did that, particularly in the last game," Lancaster said.
"We were tested at the highest level. The final 20 minutes was the most disappointing thing about the game, to let it slip away like that.
"At 9-3 we were still in the game. We put the ball straight into touch and had a period of defence which resulted in 12-3.
"There was then a turnover at the breakdown - which we still need clarification on - and that was the tipping point in the game (because it led to Wales' first try).
"Whatever happened in that breakdown it was disappointing to lose composure and let the game slip away.
"Our ability to retain our composure in the heat of battle (is one of the biggest lessons to take from Cardiff)."
The other is execution. Manu Tuilagi should have scored in the opening minutes but he knocked the ball on and too often England forced offloads or lost the ball in contact.
"Everything matters in the game, whether it is the first minute or 21st minute, you have to take your opportunities when they are presented," Lancaster said.
Overall, Lancaster felt his side had made progress and he was proud they had put themselves in with a chance of winning the Grand Slam.
Lancaster will now use the summer tour of Argentina to uncover new talent, to develop some of England's rising stars and increase the depth of players available.
"Overall when you look at the campaign we made good progress," he said.
"We have a good group of players and we played some tough games during the Six Nations and to put ourselves in a position to win it was hugely pleasing.
"The next step is for our best players to go to the Lions and see how they develop under that pressure, which will be significant, and for Mike Catt and I to take another group of players to Argentina and make sure we get that depth of talent we really need to see emerge.
"It will be critical for us because we go to a hostile environment and put ourselves under pressure. That is why we want midweek games as well.
"It gives us a chance to work with a wider group of players and which players can make the transition from club to country and play and deliver in a hostile environment."
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