When Billy Vunipola plays well, England win. That used to be the rule of thumb.
When he rocks and he rolls, Vunipola becomes such a momentum magnet that England are unstoppable.
He has long been a barometer for England’s fortunes. So it follows that in the past year he has been ordinary and so have England.
What happened in Cardiff yesterday then defied convention. Billy rediscovered his punch, yet England ended up on the canvas.
The Saracens forward carried 15 times and made 94 metres – 93 more than he had in England’s previous two games.
He caught the eye left, right and centre, forever in the thick of the action. Yet when the whistle went Wales were handed the Triple Crown.
Worse still, the man of the match award went to a number eight but it was Taulupe Faletau, Vunipola’s cousin.
The truth is that having admitted to letting down his team mates with a number of “rubbish” performances over the past 18 months, he was let down here.
England have become too desperate to find the long-lost magic of their World Cup semi-final win over New Zealand. Their discipline is shot, their penalty count off the charts. Fourteen here, five alone by Maro Itoje.
But you can’t be too scathing. They were grievously wronged by two shocking decisions that allowed Wales’ first two tries to stand.
They didn’t hide or spit their dummy. They fought back admirably from 17-6 down to level at 24-24 with 18 minutes to play.
Vunipola was central to all of that. A player transformed as England railed against the injustice of referee Pascal Gauzere’s calls.
He wanted the ball, sought the collision, started eating up ground as England played through their rage and found their form.
When Ben Youngs sniped his way over on the hour to level things up it seemed Vunipola would get his just desserts.
And perhaps in normal times they would have done, with the growing frustration of a full house suffocating Wales’ in the final quarter.
But England could count on no outside help and as the game ticked on, fell victim to the indiscipline which dogs every team on the slide.
Having steered Bristol to the top of the Premiership, Callum Sheedy came off the bench to guide Wales to glory.
Three times his unerring boot feasted on English failings, before converting Cory Hill’s late try to put the tin hat on it.
England were nothing like as bad as the scoreline suggests and Billy Vunipola was a good deal better.
But that counts for nothing today as Team Jones lies fourth in the championship with France and Ireland still to play.
Big Billy is back, but England’s form has left town and taken hope with it.