In the immortal words of former US defence secretary Donald Rumsfeld, "there are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know.
Who knows what he was talking about, but in the "we don't know, we don't know" category you can add "likely World Cup winner".
The only known known when it comes to the Rugby World Cup is that Ireland's victory over Australia has thrown the cat among the pigeons.
And the wise man's pick of Australia to win it all is looking a bit dodgy. In fact, anyone's pick is starting to look a decidedly wobbly.
Australia looked to be moving nicely into its work in the second half of its first game against Italy.
But it was found wanting on Saturday night.
Sure, the Aussies have some quality players. But they also have some real holes which were exposed by the Irish.
Combine an average scrum, with some poor players in key areas, and a referee on their back, and all of a sudden the Australian ship struck some heavy water.
The thing to note about this tournament is that it is test rugby. It is not the fancy Super 15, where there is more space, and plenty of chances to run.
Test rugby is exactly that - a test, where things are much tighter and the basics have to be fundamentally strong. Scrum, lineout, tackle - the Australians were not on the button in these departments on Saturday night and that is why they lost.
Now, instead of the dream final between the Australians and the All Blacks, these two teams may not clash at all.
The Wallabies look very likely to meet South Africa in the quarterfinals and judging on Saturday's form, the Australians are going to struggle. They will urgently need to get some strength into their scrum.
The men from the high veldt are working their way into form nicely, though why Fiji tried to play them in a physical match is a puzzler.
There are still questions about whether South Africa is quick enough and agile enough against a side which can keep the ball for long periods.
As for the All Blacks, little could be taken from their game on Friday night. They played Japan B and should have won by plenty. And they did.
But a win like that does help with confidence and that can only be a good thing.
This Saturday night's game against France is a big, big game.
A solid performance and a win will have everyone tipping them as the favourite.
Just like Australia a week ago.
Our Col
Colin Slade did not convince against Japan B. But he did not play a shocker either.
A real mixture. Good and bad. He got better as the game went on but so did the whole team.
Everyone else seems to be struggling with goal kicking in this tournament so why shouldn't he?
But with the crunch games looming, Piri Weepu is likely to be the reserve No 10 on the bench. And he could start if Dan Carter can not shake off his back injury.
Argy bargy
All of a sudden the Four Nations next year looks like it will be most interesting.
After running England close, the Argentinians were convincing winners over Romania in Invercargill on Saturday.
Considering this is only the third time the Pumas have played in the past year, they should be a formidable force next year.
The only doubt is whether all their players will be available come next year.
Questions
1 Zac Guildford - will he be the Frano Botica (as in, non-playing reserve) of this squad?
2 Could those Irish green jerseys be any tighter? Some of them looked like they had been painted on.
3 Fetu'u Vainikolo, Shaun Webb, Alapate Fatafehi, James Paterson - all players who have under-performed when playing rugby in the south in past years. But they are all at the World Cup. The cream may be on show in this tournament but is there also a sprinkling of spoiled milk?