There was a theory that did the rounds during the 2015 World Cup that the reason England's bowlers persisted with the slower-ball bouncer was that, when they attempted the delivery in the nets to their own batsmen, it worked a treat. It's just that when they tried it against almost every other side's batsmen, it was thrashed into the stands.
Maybe it has been the same with Mark Wood in the Test series against South Africa. Had Wood been bowling to his team-mates at Trent Bridge, he might have had a hatful of wickets. But as he was bowling against men who were prepared to graft through tough periods, men who were prepared to play the ball on its merit and who sell their wickets dearly, he has been left empty handed. The only wicket he has taken in the series has been that of JP Duminy - something of a mercy killing, really - and that was with a long-hop. His average for the series - 197 - is so ugly it only goes out under cover of darkness and wearing a broad-brimmed hat and sunglasses.
Wood hasn't bowled badly, by any means. While his speeds have not, perhaps, been quite what they once were - or at least what once was hoped of from him - he has still bowled the quickest delivery by an England seamer in the match (90.1 mph in the second innings; Ben Stokes was quickest in the first with a delivery of 88.6 mph. Chris Morris - at 92.5 mph - has been the quickest in the match so far) and, while he has been hit for more boundaries (22) than any other England seamer in the match, his lines and lengths have been reasonably good.
But Wood is meant to be a weapon of shock and awe. Not dull and bore. And as South Africa's second innings started to shut the door on England, it became increasingly apparent that Wood didn't have the keys to unlock it.
It wasn't the first time, either. Wood was relatively anonymous at Lord's. While he was, again, the quickest member of the attack, it was only by 0.1mph from Stokes. And that's not enough to count as a point of difference. And if he isn't offering anything different - anything explosive; anything that can threaten a breakthrough on flat surfaces - his value to the side is vastly reduced.
There are other bowlers - the likes of the injured pair of Jake Ball and Chris Woakes - who can offer control. And while Wood has gained a little swing in the first innings at Trent Bridge, it has tended to be early and predictable. Again, Woakes and Ball can probably provide that skill more reliably.
The man who Eoin Morgan turns to in white-ball cricket - the man who dismissed Kane Williamson with a snorter (albeit one that may have benefited from some assistance from the pitch) in a key Champions Trophy match in Cardiff - has regularly looked the most innocuous member of England's seam attack in this series. Instead, it was Stokes who produced the stand-out spell of the third day. A spell of nine overs for eight runs that included the wicket of Dean Elgar caught fending off a bouncer. It was exactly the sort of spell England hoped for from Wood. And if Stokes can provide it, England may well be better served looking for a bit of variation from another source.
There are several caveats to all this.
The first is that South Africa's batsmen have played excellently. Elgar and Hashim Amla in particular - Heino Kuhn, too - have demonstrated the discipline and patience that England's batsmen should have shown in their first innings. They have played the moving ball like experts and put a much higher price on their wickets.
The pitch has also slowed. Whatever moisture might have been in it at the start has long since departed and, while there is a little movement on offer, batting is certainly easier against an older ball. And Wood usually has to wait a while before he gets his hands on it.
It might well not be the sort of surface that suits him, either. Wood appears to be at his most valuable when the pitch is flat but offers some pace. He can, when conditions suit, gain dangerous reverse swing and he can, when conditions suit, generate pace and bounce from a length that few bowlers in England can match. This surface increasingly seemed to suck the energy out of his bowling. It will be interesting to see how Morris copes on the fourth day and it doesn't necessarily mean Wood won't be useful in Australia.
Wood is feeling his way back after injury. The Lord's Test was his first since late 2015 and, when a man has had three operations on an ankle within a year, it is only natural there is to be some hesitation, perhaps subconsciously, when he returns. He has admitted he thought he may never play Test cricket again. It may take a while for him to regain full confidence in his body.
The England camp also reported that he had a bruised heel towards the end of the third day. While they specified that there was nothing the matter with his much operated upon ankle, it seems fair to conclude that his performance may have been inhibited a little.
Is that last one a caveat? The worry remains that Wood simply doesn't have the frame for the rigours of Test cricket. Certainly back-to-back Test cricket. Or that those injuries have robbed him of that little bit of magic - that extra one or two percent - that gave him that point of difference. Either way, it might well be a mistake to consider him for back-to-back matches in future.
And while he might still have a valuable role as a squad player, it really does seem optimistic to the point of recklessness to expect him to be at his best in all five Ashes Tests in a few months' time.
There is some encouraging news for England. Woakes takes another step on his recovery on Tuesday when he plays for Warwickshire's Second XI in their Championship match against their Durham counterparts. But he is appearing only as a specialist batsman and, with Warwickshire not playing another first team Championship match until August 6 - the final Test starts on August 4 - he will have very little chance of gaining match-readiness before the end of this series. The window created for T20 cricket has some pretty obvious downsides.
Wood, to his credit, has shunned the option of life as a limited-overs specialist. Even on the eve of this match, he spoke of his hunger to prove himself as a Test player and he doesn't seem the sort to change his mind after a tough few days at the office. The fact is, though, he had a relatively short window of opportunity in which to prove himself as a first choice and, right now, he hasn't been able to take it.