TWICKENHAM, London - The fine margins of sport were on full display at Twickenham, as Wales took England the distance once again. But just as they did two years ago, when George North may or may not have been in touch at the final whistle, they will head home with a feeling of 'what if?'
Had a first-half TMO call gone their way, had Scott Williams not dived for the line prematurely or had Gareth Davies spotted an inside line a split-second sooner, would their Grand Slam hopes still be intact?
Warren Gatland and his coaching staff would be within their rights to ponder those very situations. This was not a defeat to be ashamed of when you are missing at least seven of your first-choice starting XV, and your ace goalkicker and fullback is a late withdrawal.
But those questions do not do justice to the strength of character and conviction - not to mention the depth of Eddie Jones' squad - that were displayed by England in order to get over the line at Twickenham.
Amid the most inhospitable of February conditions in south-west London, Jones' side stamped their authority on the contest early and then proceeded to keep their visitors at arm's length. This performance might not live in the memory past Monday but it was every bit as impressive as the seven-try mauling of Italy in the Rome sunshine six days earlier.
It should have come as no surprise that England looked to put pressure on Rhys Patchell - and late addition Gareth Anscombe - in the opening stages given what had been said during the week.
And it was a ploy that paid early dividends as the rain came down at Twickenham. Owen Farrell had already rattled Anscombe when Anthony Watson put in an excellent chase that knocked a dropping ball away from Patchell as he went to gather.
Farrell latched onto the bouncing ball, spotted an ocean of space in behind the Wales defence and arrowed in a kick that Jonny May gleefully ran onto to score, crucially timing his slide to perfection in the exact same area of the field where Williams would later be denied.
Patchell was finding Twickenham a lonely place, and moments later he would drag a penalty attempt wide of the upright. It was not the nerve-settler he or the Wales coaching staff would have hoped for.
England sensed their chance and following a mammoth 25-phase attack inside the Wales half, Joe Launchbury displayed the skill of an All Black to take contact and offload inside for May to scamper over for his second try of the game.
It was not a tactic that would work for a full 80 minutes, and Wales would end the opening 40 minutes in the ascendancy. They quite possibly should have had a try of their own too, but TMO Glenn Newman decided that Anscombe had not clearly grounded the ball after it had deflected off Steff Evans' knee. The debate on that particular moment will run and run, possibly all the way to the end of a tight championship.
With an advantage coming, Patchell would get his side on the board from the tee but there were groans from the majority of the 82,000 fans inside Twickenham as he did so, with Wales captain Alun Wyn Jones alerting referee Jerome Garces to England's mounting penalty count. It got the backs up of the locals, who sided with "Uncle Eddie" and his complaints over Wyn Jones' influence over officials.
England would turn around 12-3 in front but they would need to draw on every ounce of their defensive fortitude to maintain that lead as a bitterly cold wind swirled around Twickenham in the second half.
They would also need to call on their reserves, literally. Sam Underhill and Jack Nowell were both called on early in the second half, as Chris Robshaw spent much of the second half packing down in the No. 8 position at scrum time.
The usual 'finishers' - Jamie George, George Kruis et al - allied with a few less familiar faces provided ballast and impetus from the bench. A little over 18 months from the Rugby World Cup in Japan, Jones is building his squad nicely.
Wales were thwarted early in the second half as Aaron Shingler elected to kick through rather than look for a pass to Gareth Davies, though the scrum-half did not help his teammate out with a poor choice of angle in support.
But this is an England team built on the dark arts, on putting in hits and putting in a shift. As man of the match Mike Brown said post-match, "you work hard, you get your luck". England did the former and earned the latter. It is notable that England do not have a specialist attack or skills coach. They do have separate defence, forwards and scrum coaches, though - these are the situations Eddie Jones' men live and train for. It pays dividends on matchdays and in matches as tight as this.
The training goes deep. Sam Underhill had only been introduced at halftime and was 20 minutes into his home Six Nations debut when he contributed a match-winning tackle. Had Scott Williams backed his pace for the corner, Wales may well have left Twickenham with more than a losing bonus-point. Instead, he went to ground, hoping to slide in from around five metres out, and Underhill delivered a stirring tackle to drag the Welshman into touch.
Gatland's side deserve credit for the way in which they acquitted themselves in the second half, though. Despite sacrificing Patchell and moving Anscombe to fly-half, the men in red continued to monopolise possession as they looked for a crack in the English defence.
Wales will not be happy with the result, nor the TMO's part in it, but there is plenty to work with as they prepare for a trip to Ireland when the Six Nations resumes in a fortnight. Patchell did not enjoy his finest evening but he will be back, this experience will only aid his development. They had not been expected to challenge for the championship before a ball was kicked, but Saturday provided proof that there is depth in the Welsh game, too.
England will enjoy this win, but they know further tests lie in wait as they bid for a third successive title. Edinburgh and Paris beckon before Ireland visit Twickenham on Super Saturday to round out the championship. Expect Jones to double down on the hard defensive yards in training. It may yet prove pivotal again.