Eddie Jones rued mental flaws in an England side which "got out of jail" in a 38-38 draw with Scotland.
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 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."
There were mixed emotions for Scotland head coach Gregor Townsend afterwards.
Scotland retained the Calcutta Cup, won 12 months ago at Murrayfield, but missed out on a famous win.
"I've never been involved in a game like that as a player or a coach," said Townsend, a member of Scotland's last championship-winning team in 1999.
"It's the most unusual game I've been involved in.
"I'm very happy with the draw considering what happened in the first half, but the players are absolutely gutted.
"They're really disappointed not to have won, which seems incredible to think when you're 31-0 down.
"We talked about winning back respect in the second half.
"Winning the second half was going to be a huge challenge, against a team which had scored 31 unanswered points.
"To go out and score another five tries in the second half is still hard to believe."
Townsend singled out number eight Magnus Bradbury, centre Sam Johnson and wing Darcy Graham for praise, describing Johnson's try which put Scotland in front for the first time as "one of the best tries Scotland's ever scored".
"We're disappointed at the end not to have held out," Townsend added.
