There were many aspects of Ireland's nightmare performance at Twickenham that would have given Joe Schmidt sleepless nights, but above all, the one that infuriated him most was his side's poor defensive display.
The lineout struggles could be put down to a very bad day at the office and as much as that remains a concern, especially against a better Wales team this weekend, Ireland pride themselves on their defensive work.
In Andy Farrell, Schmidt has an outstanding defence coach and while his record speaks for itself, he too has had to move with the times.
Twice this year, England have highlighted chinks in Farrell's armour.
Behind the scenes, the incoming Ireland head coach has been working over-time with the players in a bid to tighten up, particularly in how they have been caught too narrow at times.
Eddie Jones had clearly targeted Ireland out wide and the wake-up call they got as a result could turn out to be a blessing in disguise before they arrive in Japan next week.
A 67% tackle rate was one of the lowest during Schmidt's tenure, which naturally led to the worst defeat.
Even taking into account the fact that Wales were seriously below strength last week, there were noticeable improvements in Ireland's defensive play.
James Ryan set the tone with a typically barnstorming display as he repeatedly hammered off the line and shut down the Welsh attack.
Bundee Aki endured a tough afternoon in the thumping defeat to England, but the Connacht centre was back to his best in Cardiff.
Aki's excellent performance was such that it highlighted the importance of having an imposing inside centre who is working in tandem with his out-half and those outside of him.
It was no surprise then to see that Ireland's tackle rate had risen to an impressive 92%, which is the kind of figure that Schmidt demands from his players.
Johnny Sexton and Robbie Henshaw are two of Ireland's main defensive leaders and given how well they both communicate to those around them, the Leinster duo's return should improve things, too.
That narrow defence was also a problem for Ireland throughout the Six Nations. You can be sure that hasn't gone unnoticed by Scotland, who will look to derail Schmidt's World Cup plans in the opener on September 22.
A full-strength Wales team will also provide a stern test of Farrell's defence and if they manage to come through it relatively unscathed, suddenly confidence has been restored.
Of all the players who could potentially have suffered a dip in confidence as a result of the Twickenham horror show, Jacob Stockdale would have been right up there.
Since breaking on the scene two years ago, everything the Ulster winger has touched has turned to gold, but this was a real eye opener for how quickly the tide can turn.
In Stockdale's defence, the system inside him failed, which left him stranded out wide as he was forced to bite in on the England attackers.
Interestingly, Ronan O'Gara, who knows a lot more about defensive systems, didn't quite see it that way.
"People were saying it was very harsh on him, I didn't think it was too harsh. I thought he missed the jump mentally by two or three seconds a few times, which exposed him," the former Ireland out-half told Off The Ball.
"But people were saying it was on in the inside, yes, but if you watch the people, you still have seconds to adapt, and he didn't adapt."
With defences increasingly coming off the line harder and faster, now more than ever, isolating wingers on the fringes is a vital part of most attacking game-plans.
Stockdale felt the brunt of that and came in for some harsh criticism online, but he bounced back really well against Wales to remind everyone of his undoubted quality.
Such has been his rapid rise, it is easy to forget that this is a player who is still only 23-years old.
"Obviously whenever everything goes wrong inside you, it's usually the winger that has to try and solve the problem," Stockdale reasoned.
"I could have read it better or earlier or probably hit Jonny May man-and-ball from the scrum, but I just missed it by about half a second. That can happen. Andy Farrell was brilliant. He went through each individual thing with me.
"He did say 'This was my fault, that wasn't my fault'. But he also did give me a work-ons with things I can do better.
"It's about problem solving together. Whenever guys are talking, it obviously makes things a lot easier."
Ireland have already proved that they can repel the best attacking teams in the world and as they look to recapture that kind of solidity, all eyes are on Farrell to quickly come up with the solutions.