It was Donald Rumsfeld, the former US secretary of defence, who once said there were known knowns, known unknowns and unknown unknowns.
OPINION: He was talking about Iraq and weapons of mass destruction, but he might as well have been talking about politics and election campaigns.
The known knowns are the things governments plan for and can control like policy announcements and events that enable them to set the political agenda.
The unknown unknowns are the stories that blow up in a leader's face and are what they fear most because they have the potential to hijack an election campaign. Think the teapot tapes, Corngate, the Exclusive Brethren and Bob Clarkson's left testicle.
So with the next election now almost certain to be less than 12 months away, here are some of the known knowns, known unknowns and unknown unknowns as the countdown begins.
The known knowns
The economy – Convention has it that when the economy is on the up, the sitting government reaps the dividend at the ballot box.
That being the case the odds should be in National's favour given that the economic indicators are all on the rise and New Zealand is tipped to outperform most of the OECD next year.
Labour's challenge will be changing the conversation from one about the economy to one about living standards and tap into any burgeoning "them and us" sentiment.
That's why it has been talking about rising power prices and claiming a growing divide between the haves and have-nots under National.
The success of that strategy will hinge on the extent to which an improving economy has made people feel better off.
Interest rates – They are headed up and that will play against the Government's economic narrative
Housing – the Reserve Bank's intervention in the housing market has made it the hot-button election issue for Opposition parties to tap into.
National's dearth of allies – the fortunes of ACT, the Maori Party and UnitedFuture seem set in stone.
This is a much longer list and includes factors that are largely within the Government's control, even if they are not known yet, like the election date (the smart money is on an October election). Those which aren't include:
John Banks – if he ends up in the dock over anonymous donations to his mayoral campaign the Government will want shot of him as quickly and as painlessly as possible. One option would be Banks announcing his retirement at the next election, giving ACT time to find a new leader and further distancing him from National.
But nothing can be ruled out, including Banks resigning and either forcing a by-election or bringing forward the election date.
Kim Dotcom – the big German has repeatedly threatened to next year release evidence that will make a lie of Prime Minister John Key's repeated denials that he knew all about Dotcom long before police raided his Coatesville mansion at the request of US authorities.
Key seems supremely confident that this is a known known and that Dotcom is bluffing.
But the internet entrepreneur's wrecking-ball tendencies mean one can never be sure. Put up or shut up time is rapidly approaching, however.
Spooks – The Government Communications Security Bureau has been Key's Achilles heel this term and more damage could yet be done if New Zealand is dragged into the widening controversy surrounding the Edward Snowden documents, which have embarrassed Australia and the US by revealing the extent to which they spied on friendly governments.
Key hinted this week that some documents were already in circulation and appeared determinedly blase.
But given the likelihood that the GCSB has been spying on our Pacific neighbours for years and by extension Japan and possibly even China's diplomacy in the region Key's nonchalance may be more braggadocio than anything else.
Genesis – will selling the last green bottle on the Government's asset sales wall tip the voters over the edge from just annoyed, to angry enough to lodge a protest vote?
Unlikely but something for the Government to consider.
The unknown unknowns
Colin Craig and the Conservative Party – So far Craig has come across as mostly naive and somewhat eccentric but it is potentially a short ride from there to loopy under the magnifying glass of an election campaign.
National's experience on the campaign trail in 2005 when it was spectacularly wrong-footed by the Exclusive Brethren should be fair warning to its MPs that any courtship with the Conservatives should be preceded by a fair degree of due diligence.
Craig may not seem particularly threatening but questions will be asked about who will be riding his coat-tails into Parliament.
The Labour caucus – with his MPs still seemingly pulling in two different directions, and David Cunliffe yet to prove he has won over the doubters in his caucus, sabotage can't be ruled out.
Scandal – A Len Brown-sized sex scandal or similar on the campaign trail involving one of their MPs would see Key or Cunliffe immediately lose the initiative.
Events – Former British prime minister Harold Macmillan has been quoted as responding "events dear boy, events" when asked what blew governments off course. There isn't a leader in recent memory who wouldn't agree.
Helen Clark was ambushed over genetically modified corn in 2002 and ended up with a dramatically different government to the one everyone expected.
Don Brash nearly stole the election in 2005, but was derailed by revelations about a smear campaign launched by his secret admirers, the Exclusive Brethren.
Key was sailing high on the campaign trail in 2011 until he lost his rag over cameraman Bradley Ambrose recording a conversation between him and Banks and inadvertently breathed life back into Winston Peters' political career.
With the polls showing that the next election is finely balanced, these are the things that will keep Nat MPs awake at night.
- Fairfax Media