Just as you wouldn't go to your butcher for your eye surgery or your vet for your vegetables, so you shouldn't be asking a middle-order batsman to open the batting in Test cricket.
Yes, we know Jason Roy can do the role in ODI cricket. But ODI cricket is played with a Kookaburra ball that barely swings. And it's played, on the whole, on pretty flat wickets where the bowlers gain little seam movement. It is, in short, a different game.
Opening the batting in first-class cricket is a specialist role. It's not so much about the shots you play as the shots you don't. It's about knowing which balls to leave, about having the patience to wear bowlers down and the defensive technique to withstand the moving ball. And if you don't have someone who can do that, you risk exposing a middle-order that may legitimately not have those skills, to the new ball and fresh bowlers.
While Roy could, perhaps, learn the skills required to open in Test cricket, expecting him to do so at this level - and against an attack as good as this - is naïve to the point of recklessness. He does not open for England Lions and he does not open at county level. While Surrey did, briefly, experiment with him in the position, it was a ploy they abandoned in 2012. And it wasn't because he made it all look too easy. In all, he averages 31.65 in the role (which he last attempted, in just two innings, in 2015) in first-class cricket. He now has the second-lowest average (9.80) for an opener with five-plus innings in the Ashes since the start of the 1900s. Only Geoff Cook, who averaged 9.00 in the 1982-83 Ashes, is lower in that time.
Whether Roy has the appetite for the role is unclear. A couple of day ahead of this game, he spent much of his time in the nets trying to slog almost every delivery he faced into the stands. Maybe it was an exercise designed to build his confidence but, in the long-term, it is competence than breeds confidence. It rarely works the other way around.
It seems absurd that an England system that prides itself on attention to detail - this is the side, remember, that provided its players with a cookbook involving various quinoa recipes in a bid to ensure they were in optimum position - can take such a laissez-faire attitude to such a key position. And absurd they can go into such games, against such attacks - and we really do have to acknowledge that this is a terrific Australia bowling line-up - with such a makeshift solution despite their coach acknowledging ahead of the game that Roy is, in his view, better suited to the middle-order.
So it was irresponsible to pick Roy for this role. Just as it was irresponsible to ask Ollie Pope to bat at No. 4 - a position he had never fulfilled - in the Test series last summer. Pope, you may recall, came into the Test team having never batted before the 20th over of a first-class innings. He was used to batting at No. 6 for Surrey.
On both occasions, the over-promotion of Roy and Pope risked ruining a talented player. Nathan Leamon, the sometime England analyst, has previously talked of data that suggests that the longer it takes new players to achieve success, the less likely it is they will go on to enjoy long careers. Destroying players' self-confidence in the formative stages of their career could cause lasting damage. The fact that England are considering swapping the positions of Roy and Joe Denly - who looked so out of depth while batting on Friday that it was tempting to call the coastguard - is not especially encouraging.
In truth, Roy is probably not well suited to batting at No. 4 in Test cricket, either. It would be easier, for sure, but it would still require patience, technique and discipline. And while he is a man with many skills, the stroke that brought his dismissal here - edging a drive at one outside off stump that left him a fraction - did nothing to suggest he has those qualities. He might well prove best at No. 6. But England aren't looking for No. 6s.
Conditions were pretty good for batting on Friday. Yes, the attack was good and there was seam movement. But it was sunny and there was none of the swing that troubled batsmen on Thursday. England would be deluding themselves if they hid behind the conditions as a reason for this capitulation.
Ed Smith, the head selector who has pushed for Roy to open, Pope to bat at No. 4 and Denly to win an extended chance in the side, does not emerge from this situation especially well. He has previously defended his selection policy by stating, "there has to be a compelling reason not to have one of your top players in the team". But such a naïve policy ignores the balance required to build a side; it ignores the specialism required at this level; it involved far too much wishful thinking. It just isn't working.
Ultimately, though, all these issues stem back to one fundamental problem: county cricket does not appear to be producing top-order batsmen of the quantity or quality required. Until they do, England's team management will always be looking for contingencies and England's middle-order will continue to be exposed. Eventually, the penny will drop at the ECB, that by eroding the primacy of the county championship, they have eroded their Test team's ability to compete. They are the ones to blame for these embarrassments. The team is simply the product of a broken system.
There are, however, some other options. There's Dom Sibley, of Warwickshire, who has churned out runs consistently over the last year and has the patience of an old-school opener. There's Zak Crawley, who looks a fine talent and plays the short ball particularly well, but who is very young, very green and, perhaps, a little vulnerable to expose at this stage. And there are the likes of Sam Robson and Mark Stoneman whose averages in the high 20s or low 30s are suddenly not looking all that shabby.
But increasingly, as you cast around the counties for options, you are reminded of Bob Dylan's great line: "All these people that you mention, I know them they're quite lame, I had to rearrange their faces and give them all another name." It probably won't matter too much who England pick. The system is broken.
Sound like hyperbole? Well, this was England's lowest Ashes total since 1948 and their second-lowest since 1909. It was the fourth time in the Trevor Bayliss era that they have been bowled out for under 100; no other Test side has suffered such an indignity so often. It keeps happening. And if things keep happening, they can't be dismissed as an aberration.
There is a lack of respect for the old virtues of batting; for determination and patience and technique. And there is a lack of respect given to the county game which builds players; truly, the changes made in recent years amount to an act of vandalism. If the ECB truly care about Test cricket - oh, they talk a good game, but there's very little evidence of anything other than talk - they will acknowledge that you don't build Test success by focusing on white-ball cricket and you don't build a team by picking the most attractive stroke-makers. The ECB's policies played a key part in winning the World Cup, but are about to play a key part in losing the Ashes.
England's Test batting is painfully weak. Perhaps as weak as it has ever been. Unless the ECB have the courage to change the county structure - and yes, that includes backtracking on the monstrosity that is the white-ball window and accepting that the focus on The Hundred won't do a thing to help the Test team - it will keep happening.