Eddie Jones rued mental flaws in an England side who "got out of jail" in a 38-38 draw with Scotland, and admitted his side must now "dig deep".
England's Six Nations title hopes were over before kick-off due to Wales completing the Grand Slam in Cardiff. Jones' men brushed off the disappointment by racing to a 31-0 lead in the Calcutta Cup clash.
However, England imploded and Scotland led 38-31 into added time, on the cusp of a first Twickenham success since 1983. But George Ford crossed and converted his own try for a 38-38 draw.
"It was 100 per cent mental. There's no physical difference out there at all," Jones said of his side's final competitive game before the World Cup begins in Japan in September.
"It's not something you can fix easily but we know what the problem is... It's going to take some digging deep into the team psyche but I think it's a good lesson for us before the World Cup.
"It's a bit of a recurring theme for us. We've experienced this at least three times in 12 months, where we've taken control of a game, let our foot off the gas and then been unable to get control of it back.
"Our first half there was some exceptional rugby. We should have been ahead by a lot more. We came in at half-time determined to play a bit tighter and with a bit more discipline, but we failed to do that.
"It's a great lesson for us. I thought our finishers (replacements) did exceptionally well to get us out of jail at the end. Obviously, just disappointed with the full 80 minutes."
England's only loss came in Cardiff, where a similar collapse proved costly as Jones' men ultimately finished second in the championship.
Jones added: "It's never one thing. It's always a combination of things. Just lacking that discipline to do the simple things over and over again.
"We got seduced by the scoreboard. And sometimes it can be one player that does it and then it becomes infectious.
"There's not one area we need to fix, apart from our ability just to be able to regain ourselves.
"If you look at our tournament, apart from a poor 30 against Wales and a poor 40 against Scotland, we've had a pretty good tournament."
Jones clung to the positives of experiencing the setback now, rather than in Japan.
He added: "We're all disappointed, players, coaches, we're all disappointed. But it's a lesson. And the hardest lessons are the best lessons. And you want these sorts of lessons before you go to the World Cup.
"Because you do that in the pool game against Tonga, for instance, then you can find yourselves in a difficult situation going forward.
"So we'd rather have those lessons now and we'll do everything we can to learn from them and make sure it doesn't happen again."
England captain Owen Farrell, meanwhile, struggled to explain what had happened during the second half.
"It shocked us when they got a bit of momentum. We probably allowed them to play a bit too much. We got in a momentum rut and we couldn't get out of it. It was probably more in our control than we thought.
"The halftime score was pleasing but Scotland were good in the second half. They played some good rugby and punished us.
"All we've got to do is learn and improve. We will have to look at ourselves a bit deeper and perhaps that's a good thing."