Reason: Rugby replacements rule has its flaws
You can blame the goal kicker, you can blame the concession of daft technical penalties or a single colossal blunder at the wrong time.
It's hard to argue. But the single main reason why Argentina's strong men could dominate South Africa the other weekend and still end up losing was the train of Springbok replacements.
Coach Heyneke Meyer hooked beaten players from the pitch and sent on an eager second wave of men like Adriaan Strauss and Tendai 'the Beast' Mtawarira.
If ever the eight replacement rule was shown to make a mockery of the game, the second test between the Pumas and the Boks in Salta was the occasion to make the IRB reconsider the unjustness of the regulation.
You may argue that it is the same rule for everyone, but it is and it isn't. Yes, Argentina could also have emptied their bench, but what good would it have done them.
Teams like Argentina, Italy, Samoa, even Scotland these days, simply do not have the strength in depth of the major rugby playing nations.
The eight replacement rule makes it even harder for them to cause an upset.
Argentina have a mighty pack. Each of their eight forwards plays top level club rugby in either France or England, the two strongest leagues in Europe. They are formidable players.
Thanks to Steve Walsh, a referee who knows how to ensure a fair contest in the scrummage, Argentina's pack destroyed the Springbok eight.
Because Walsh stopped Jannie du Plessis cheating at the very first scrum, the Argies were able to drive through South Africa. The week before they had demolished the first scrum of the game, and then the ref allowed South Africa's front row to turn in and neutralise the shove.
Walsh was having none of it. He made South Africa stay straight and they were pulverised. One scrum into the second half and Meyer had seen enough.
After 45 minutes he sent on Frans Malherbe for Jannie du Plessis and Mtawira for Gurthro Steenkamp. On 51 minutes he put on Strauss for Bismarck du Plessis and Marcel Coetzee for Juan Smith.
South Africa now had an entire new front row on for the final 30 plus a driving back row forward. Doubtless Meyer would also have sent on Bakkies Botha at this point if he hadn't needed to keep one forward back in case of injury.
Argentina have no chance of matching such quality.
Four of their five forward replacements still play club footie in Argentina. Only back row forward Leonardo Senatore plays in the English league. Argentina's dominance in the scrum was reduced to a slight edge.
But still the Pumas came on, assisted by South Africa's appalling kicking game. Enough already, said Meyer.
On came Morne Steyn for Handre Pollard and Francois Hougaard for Ruan Pienaar. Meyer was losing the game of chess. So he gave the board a good nudge and changed the pieces.
The scrum was saved. Coetzee started to get some carry over the gain line. Steyn's passing created one try and the new wave of forwards rolled a maul over the line for another try. Oh, and Steyn also kicked a crucial conversion from the right touchline.
The introduction of multiple replacements into rugby has disadvantaged the weaker nations, but there are plenty of other reasons to bemoan its introduction.
Once upon a time guts and stamina mattered.
Players were partly selected on their ability to go for 80 minutes. The halfback (the position shown statistically to have the biggest all-round running load) or flanker with a good engine could gain an edge later on.
A Will Genia might wait until the 70th minute before playing his hand, but then he was gone, speed and fitness taking him past the opposition defence. Graham Mourie was known as an 80-minute player.
Perhaps Richie McCaw would have been even more dominant if the opposition had not been able to freshen up after 60 minutes.
The old requirement on players to last a whole match may also have some bearing on the fact that the average size of players was smaller before replacements came in.
The offensive tackle in American football is over 135kg. He is built to destroy. He is built to hurt. But he simply could not carry so much power if he had to last for 80 minutes.
So if you reduced the number of replacements, you may also reduce the number of injuries.
As yet there is no good research on that, because there are certainly counter arguments. But when rugby league went from unlimited interchange to limited interchange, they recorded a 30 per cent reduction in injury.
I like the comment of one rugby league head who posted on the reduction in rolling subs, ''As an antediluvian who can remember when every player had to play 80 minutes unless carried off I welcome the changes.
''Oh for the days when guts and determination, allied to fitness, sorted out the men from the boys. You may get a better spectacle nowadays but many a 'flash' team lost out in the last 20 minutes to cussedness and courage.
"Sorry for the rant, from an old codger, sucking on his bread and milk.''
It is hard to imagine Argentina beating New Zealand this weekend.
The inexperienced ref Pascal Gauzere will allow the All Blacks to angle in at the scrummage if it becomes an issue. And then there's the All Black bench with the likes of Beauden Barrett, Sam Cane and Steven Luatua.
Shock and awe. Don't expect the imperial armies of rugby to give up its weaponry.
South Africa, England, France and New Zealand like having a reserve army. It's a numbers game.