Wales stormed to a record 30-3 victory on Saturday to retain the championship crown and inflict more last-day misery on England, who also lost Grand Slam deciders in 1990, 1999, 2000, 2001 and 2011. Lancaster conceded his side's lack of experience cost them against a Wales side who have now won four titles in nine years.
"It is difficult (to take it on the chin) but when I look back and try and put some perspective on it - the four wins and the New Zealand game and building as a team - there is still an upward curve," Lancaster said.
"We are still developing experience in a young team. What told (in the game) was a few things and one of them was experience. We will be better in the long run. The players are hugely disappointed. They feel they have let themselves down, that they have let the country down and it is a difficult place to be.
"I try and pull them back to the perspective that we had fewer than 300 caps going into a game of this magnitude and how much we have developed in the last 14 months. No team goes unbeaten in international sport. The difficult thing for us is we don't meet again until November. It is a long time to wait.
"I do believe the journey we are on and the plan we have is the right one. We had a lot of over 30-year-olds at the 2011 World Cup and we needed to develop new players. We have had more ups than downs. This is a down but we will hold our nerve and stick with the plan because I believe it will come good."
That is not to say Lancaster will simply plough on. The England coach will enter a period of self-reflection before he begins to build towards the summer tour of Argentina.
"We are all in it together. It is not just about the players. I need to look at what we did during the week and how we prepared for the game and everything else," Lancaster said.
"I will always look at myself first. It will be tough but I knew when I put my hand up for the job that there would be tough times along the way.
"I had some in South Africa (on the summer tour) and in the autumn internationals and you look inside yourself to see what you can do better."
- Sports & Recreation