Franklin D Roosevelt is not a man I would normally turn to when trying to understand what happens on a rugby field. But sometimes you need someone who has lived through the world's toughest times to give you a little perspective.
In 1933, as the Great Depression was at its deepest, the newly elected US President spoke about confidence. In his first speech to a suffering nation he explained that confidence "thrives on honesty, on honour, on the sacredness of obligations, on faithful protection and on unselfish performance. Without them it cannot live".
Confidence is at the heart of all human success, and best of all it is contagious. Take the England team, who have just turned their world on its head, putting in what many called the nation's best performance at Twickenham.
Coaches who were under growing pressure could, after that hour and a half, breathe easily again. Players who had been dodging newspapers to avoid the endless calls for change, spark and victories, were probably first in the queue for breakfast or at the newsagents on Sunday.
The doubts have gone. That nagging feeling of wondering whether you are honestly truly good enough to be an international (a feeling that everyone has no matter how talented you are) has gone.
They now know that on their day, not only can they mix it with the best, they can actually beat them. With that comes a collective shift in consciousness that will have a halo effect not just on the team's supporters but also the clubs, who welcome back their internationals this weekend.
For the England squad members the world is a better place and their club team-mates pick up on their body language. The returning heroes are not smug or arrogant, they just have an air about them. Everyone wants a piece of the action, to hear about the stories, the little nuggets of information that bring the match together, that turn it from a TV picture into something tactile, real and achievable.
Training lifts a notch. Those who are on the edge of the senior international squad raise their game because they want in. Those who have just delivered know that they want more because the drug is so intense. Those who never thought of themselves as internationals suddenly start wondering what they might be able to achieve.
They think: "He's good, but not that good, maybe I can have a crack as well."
The same players, the same teams find a new level of intensity and performance that no amount of talk or coaching can achieve in such a short space of time.
If you can feel the buzz in a pub or on the living-room sofa imagine what it is like on a training paddock. As the returning internationals run out of the club tunnel, home or away, they honestly believe they are as close as dammit to invincible. At the kick-off, the opposition seem to be moving a little slower than they were before the magic result.
Suddenly there is clarity to everything, decisions become easier, because the second that rushed past a week earlier now seems like a minute.
Decisions that were dithered over are now made with a certainty that infuses all around with trust and enthusiasm.
It also helps when things get tough because the England players, the senior players in a club side, will have a mental photo they can return to and shore up their team-mate's fears.
The players who haunted their dreams for so long are suddenly less frightening. And as fear fades so performance improves.
I am counting on this confidence effect being evident across many of this weekend's matches, and nowhere more so than in Saracens' game with Munster today, because while England had their New Zealand, Ireland had their Argentina.
For Ireland it was not so much the surprise factor but the manner of their win against the Pumas two weeks ago that cannot be overestimated.
The flow, the pace, the clinical precision. It was based around a slick flow and movement of the ball against an Argentinian team who can stifle the best in the world.
Ireland matched the physicality of one of toughest packs in the game and then shifted the ball as if they were back on a training field.
From a side where it seemed as if everyone was slightly scared, they suddenly became a team where everyone wanted a piece of the action. Players who had looked leaden-footed suddenly looked like Lions. It was an impressive resurrection that the Munster players will be keen to continue against Saracens.
It will be interesting to see which side benefit most from their internationals' endeavours because, as FDR knew only too well, all it takes is one confident man and almost anything is possible. (© The Daily Telegraph, London)